You could go into one of the text files in the game and edit it to raise the limit from 500. The altered text file is also downloadable as a whole file. Eventually the game was patched so you could use as many as 5000 units, though anything that high was kind of absurd IMO. 1000 should do it.

I was the first person who reported on TAK when it was on E3. Pretty fun playing it there. The thread got gigantic, because everyone was all excited.
The lead developer and CEO of the maker of TA was Chris Taylor, who went on to make Dungeon Siege and Supreme Commander. It was an artist/designer on TA who went on to make TAK after Chris Taylor had already left Cavedog.
TAK's art was great at that time, but with almost nobody having anything like broadband back in the day, and memory being so pricey and still insufficient for some games (2 gigs cost a lot, was the max computers could hold, and was the minimum to play TA and other RTS games with no slowdowns back then), well ... the game lagged like hell for pretty much everybody at least much of the time. We got art but sacrificed fluid gameplay. And yeah, the resource model simplification wasn't an improvement.
Chris Taylor made a number of games, including a baseball game and I think a boxing game before he made TA.

Wait, what now? 2 GB RAM being the minimum to play a game from 1999 without slowdowns? I guess that means to play Supreme Commander you need at least 20 GB then.

I bought TA:K retail and didn't like it. Just played a couple of missions. I didn't like playing different races back and forth and the sound effect of the crow... man, that was annoying. It sounded like a guy trying real hard to sound like a crow and every time you clicked on the stupid birds, they would make it.
Also, the whole build a unit and once you build the next unit, it so tops the previous one it makes it useless. I'm very stuck on that Starcraft principle where units should have their niches or roles and not be made completely obsolete by other units.

Yup, get 500 or 1000 3D units going, each moving along different vectors, and it eats up a lot of memory. All RTS games with high unit counts are extremely memory-intensive, and ones with anything 3D in them, all the more so. AOE 2, which came out not long after, was the same way. Without 2 gigs, you could expect slowdowns.
If you slowed people down and made their game skip while your computer was trying to read info from your hard drive (virtual memory), it was pretty hard to get into a good guild, too.

Did anyone even have 2GB of RAM in 1999? That was the year I went off to college, and I ordered myself a gaming PC for like $1500, and it had 128MB RAM! (Celeron 466MHz, TNT2 Ultra, Windows 98 SE - those were the days.)

What are you talking about? Most maps needed about 32MB. Some needed 64. I ran the game just fine on 16MB on most maps. Were you running Norton in the background or something?

Hmm, maybe he meant "2 gigabits"?

He could probably have managed on 64MB, to be honest. TA was of an age where developers actually overestimated the system requirements.

I assume that the issue with the music playback still isn't solved? I wouldn't want to burn the game on a CD just so that I can listen to the soundtrack. And TA without the orchestra ... isn't really TA. :P

Music plays during the game all right for me.

Nice. Does it simply play one track after another, or does it switch for combat / building?

Music working perfectly here. Weird how it is not playing for you. Maybe... turn your speakers up :P [/joke]

This is going to make me sound like a heretic, but I'm the rare egg who marginally preferred TAK over the original TA (which is obviously a great RTS). I'm the sort of gamer who prefers the S over the RT, and the big problem I have with a lot of RTS designs is they quicky devolve into speed-demon clickfests (read: Starcraft) once the players understand the basic game mechanics. That's not for me.
TAK's overriding design principle was to maximize the strategic element by having multiple factions from the start (4 in the basic game, 5 with the expansion), each of which having very different unit sets and different technology trees. Preferred strategies were thus radically different from one scenario to the next, depending on which faction you were playing and which you were up against. The single-player campaign moved you around between the different factions, creating a lot more strategic variation in each scenario (something which Blizzard blew big time with Starcraft 2, and the biggest of several reasons I passed on it for now). Yes, the resource model was simplfied (mana), but to me that was an expected trade-off to keep the design from becoming inordinately complex. I recognize that a lot of this is possible in TA with some of the larger player mods, but I'm talking about the out-of-the box experience for the gamer who doesn't have time to delve deep into mod installs and player forums.
I never did get the TAK expansion back in the day, it came out just as Cavedog was going under, and was hard to find. So, if TAK+expansion can be made into a GOG, I'd be all over that. Perhaps more extended play might reveal it to be imbalanced, but in theory TAK is just as moddable as TA is...