I just bought Heroes 2 Gold. I own the original Heroes 2 CD but never had the expansion. One of the main reasons I wanted to buy it was the amazing soundtrack it has. However, when I start the POL campaign, I still hear the original castle music inside the Barbarian castle (track #9 on the "soundtrack" instead of track 31).
Does anyone else have this problem?

Thanks for your quick response Ralackk. I was pretty sure I wasn't the only one having this issue but hoped there was an "easy" fix. ;)
Anyway, a couple notes. I noticed that there is a MUSIC folder in the Heroes directory. It contains .ogg files used by the game. These are encoded only at 96Kbs! Now, I'm OK with compressed music but personally want it never lower than 160Kbs. I pulled out my original Heroes 2 CD and ripped it with EAC to 224 Kbps (maybe a little overkill). I discovered the MUSIC folder has the exact same music tracks as my CD so I just renamed my (.ogg) ripped files to match and replaced the music.
Now, I haven't had a chance to closely listen to my replaced files inside the game. I'm hoping dosbox is playing them back at their original quality - I should be able to find out when I get home tonight.
As a result, I can replace the music in that folder with the POL tracks if I want. Maybe a batch file to switch the music back and forth before running the game would work. The only issue I have is that the POL soundtrack files are MP3. I'm wondering if dosbox can handle those. I'd rather not convert from mp3 to ogg because I'd lose sound quailty doing that.
BTW, I think this is a great community here. I see lots of helpful posts in these forums.

I'm fairly sure that mp3 is a supported format in dosbox so that shouldn't be a problem. Also welcome to gog, it is a great community, one well worth sticking about and becoming a part of.

LOL, I was wrong about just replacing the tracks with the POL ones! Well, it takes a modified homm2.inst to do that (as Wishbone said earlier). For some reason, I can only get music to play if the files are in the .ogg format right now. MP3's just won't play. I wonder if it's something to do with the dosbox version being used? However, I *did* succeed! So anyone interested can follow these steps too but BACKUP your game folder first.
To use the POL music:
1) I converted the POL expansion music from the Soundtrack using Winlame to .ogg format. I used a high bit-rate (320Kbps) to minimize quality loss doing this.
2) I renamed those six files (see renaming scheme below) and overwrote the originals in the game directory's MUSIC folder with them.
3) I then created a custom cue file using IMGBurn with the homm2.gog file at the top and then homm2_01.ogg through homm2_42.ogg below. (I copied thils file below so you can just save this as homm2.inst using notepad and replace the existing file).
***You can use any music you like in .ogg format but if you don't use the expansion music, you'll have to make your own homm2.inst.
Renaming Scheme (after converting to .ogg):
Sorceress Castle (expansion).ogg renamed to homm2_04.ogg
Warlock Castle (expansion).ogg renamed to homm2_05.ogg
Necromancer Castle (expansion).ogg renamed to homm2_06.ogg
Knight Castle (expandion).ogg renamed to homm2_07.ogg
Barbarian Castle (expansion).ogg renamed to homm2_08.ogg
Wizard Castle (expansion).ogg renamed to homm2_09.ogg
HOMM2.INST (copy the text below here)
FILE "homm2.gog" BINARY
TRACK 01 MODE1/2352
INDEX 01 00:00:00
FILE "MUSIC\homm2_01.ogg" MP3
REM FILE-DECODED-SIZE 01:52:54
TRACK 02 AUDIO
PREGAP 00:02:00
INDEX 01 00:00:00
FILE "MUSIC\homm2_02.ogg" MP3
REM FILE-DECODED-SIZE 01:58:35
TRACK 03 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_03.ogg" MP3
REM FILE-DECODED-SIZE 01:49:17
TRACK 04 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_04.ogg" MP3
REM FILE-DECODED-SIZE 02:50:54
TRACK 05 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_05.ogg" MP3
REM FILE-DECODED-SIZE 02:36:52
TRACK 06 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_06.ogg" MP3
REM FILE-DECODED-SIZE 02:34:53
TRACK 07 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_07.ogg" MP3
REM FILE-DECODED-SIZE 02:25:34
TRACK 08 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_08.ogg" MP3
REM FILE-DECODED-SIZE 02:32:21
TRACK 09 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_09.ogg" MP3
REM FILE-DECODED-SIZE 02:53:64
TRACK 10 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_10.ogg" MP3
REM FILE-DECODED-SIZE 01:58:06
TRACK 11 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_11.ogg" MP3
REM FILE-DECODED-SIZE 02:08:28
TRACK 12 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_12.ogg" MP3
REM FILE-DECODED-SIZE 01:56:48
TRACK 13 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_13.ogg" MP3
REM FILE-DECODED-SIZE 02:07:15
TRACK 14 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_14.ogg" MP3
REM FILE-DECODED-SIZE 02:28:05
TRACK 15 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_15.ogg" MP3
REM FILE-DECODED-SIZE 01:49:58
TRACK 16 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_16.ogg" MP3
REM FILE-DECODED-SIZE 02:00:05
TRACK 17 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_17.ogg" MP3
REM FILE-DECODED-SIZE 02:10:05
TRACK 18 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_18.ogg" MP3
REM FILE-DECODED-SIZE 00:22:02
TRACK 19 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_19.ogg" MP3
REM FILE-DECODED-SIZE 00:06:19
TRACK 20 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_20.ogg" MP3
REM FILE-DECODED-SIZE 00:08:10
TRACK 21 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_21.ogg" MP3
REM FILE-DECODED-SIZE 00:57:30
TRACK 22 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_22.ogg" MP3
REM FILE-DECODED-SIZE 00:10:46
TRACK 23 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_23.ogg" MP3
REM FILE-DECODED-SIZE 00:53:67
TRACK 24 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_24.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 25 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_25.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 26 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_26.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 27 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_27.ogg" MP3
REM FILE-DECODED-SIZE 01:04:32
TRACK 28 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_28.ogg" MP3
REM FILE-DECODED-SIZE 00:06:56
TRACK 29 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_29.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 30 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_30.ogg" MP3
REM FILE-DECODED-SIZE 00:06:34
TRACK 31 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_31.ogg" MP3
REM FILE-DECODED-SIZE 00:06:38
TRACK 32 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_32.ogg" MP3
REM FILE-DECODED-SIZE 00:07:65
TRACK 33 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_33.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 34 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_34.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 35 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_35.ogg" MP3
REM FILE-DECODED-SIZE 00:06:70
TRACK 36 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_36.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 37 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_37.ogg" MP3
REM FILE-DECODED-SIZE 00:06:25
TRACK 38 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_38.ogg" MP3
REM FILE-DECODED-SIZE 00:06:48
TRACK 39 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_39.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 40 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_40.ogg" MP3
REM FILE-DECODED-SIZE 00:06:05
TRACK 41 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_41.ogg" MP3
REM FILE-DECODED-SIZE 01:18:01
TRACK 42 AUDIO
INDEX 01 00:00:00
FILE "MUSIC\homm2_42.ogg" MP3
REM FILE-DECODED-SIZE 01:16:06
TRACK 43 AUDIO
INDEX 01 00:00:00

That's strange, they updated the installers so you should have the POL music if you downloaded the latest installers from GOG. Try it again, and if it doesn't work after reinstalling, contact the GOG support. Cheers!

Personally I prefer the Succession Wars soundtrack, but POL town themes are nice too, they fit the game's datadisk theme well (Price of Loyalty, darker).