The reason why it has the Apple II Bard's Tale, is because they never made a Apple II GS version of Bard's Tale 3. This collection is the same collection/update released on the Apple iOS, iphone and ipad.
It uses the Apple II emulator, probably because well the rights to the Amiga Kickstart roms is probably way too expensive? There is only like one company that has legal rights to sell them, IIRC, and they sell them in their own Amiga game collections (which go for as high if not more than $100?). The Apple II GS emulator is also one of the easiest emulators to run, and it has good speed.
Comparably speaking the Apple II versions of the first two games are superior to the Amiga version as well, at least in sound, and for the first game a better title screen (it contains an introduction, that was left out of the amiga version).
Yes, let me repeat, the first two Bard's Tale games are the Apple II GS versions. Those have better actual Synth sound, using realistic instruments. The amiga version uses a kind of lower quality sound that sounds more like electronic bleeps and bloops but they are not 'harsh' sounding, very mellow.
Both hav the same graphics as the Amiga version otherwise, except for some minor differences (or as mentioned Amiga has a less graphically robust title screen in the first game).
The Apple II GS versions are probably the finest versions of the first two games. I don't know about the Atari ST versions but its essentially built on the Apple II/Amiga versions as well, but I don't know how its sound chip compares.
So ya, stick with the Apple II GS versions of 1 and 2, they are worth it. Avoid the Classic Apple II version of III, except only to see the alternative intro cutscene (ok, ya some might be interested to give it a go to see the other alternative artwork throughout the entire game, if you can get past the primitive coloring book appearance, and "CGA" style coloring).
The Apple IIGS' sound was provided by an Ensoniq ES5503 DOC wavetable sound chip, the same chip used in Ensoniq Mirage and Ensoniq ESQ-1 professional-grade synthesizers. The chip allowed for 32 separate channels of sound, though most software paired them into 16 stereo voices, as did most of the standard tools of the operating system (the MIDISynth Tool Set grouped four channels per voice, for a limit of seven-voice audio). The IIGS is often referred to as a "fifteen-voice system," though one stereo voice is reserved by the OS at all times for timing and system sounds. Software that doesn't use the OS, or uses custom-programmed tools (most games and demos do this), can access the chip directly and take advantage of all 32 voices.
The computer's audio capabilities were given as the primary reason for record label Apple Corps's 1989 resumption of legal action against Apple that had been previously suspended. Apple Corps claimed that the IIgs' audio chip violated terms of the 1981 settlement with the company that prohibited Apple, Inc. from getting involved in the music business.
A standard 1⁄8-inch headphone jack was provided on the back of the case, and standard stereo computer speakers could be attached there. However, it provided only mono sound through this jack, and a third-party adapter card was required to produce true two-channel stereo, despite the fact that the Ensoniq and virtually all native software produced stereo audio (stereo audio was essentially built into the machine, but had to be de-multiplexed by third-party cards). Applied Engineering's SonicBlaster was one of a few developed cards for this purpose.
