There have been quite a few threads over the past couple weeks regarding DCS and Pre-DCS sound systems. Chris Granner even chimed in on one of them. The general consensus was basically:

The DCS sound system was superior in delivering a higher quality sample, BUT the expense is that the samples are short, and the breadth and depth of the audio isn't all that great, i.e. tunes and other music hardly ever exceed 30 seconds, and just repeat.

The Pre-DCS sound system was far superior in delivering a more complete and deeper sound package, due to nothing needing to be sampled. Everything is generated in this setup. For example, White Water's score, with it's compounding rafts, would never have been possible to replicate with the DCS board, since in DCS, every raft tune would have to be a separate file in the ROM image, and you'd run out of EPROM space pretty quickly. The expense of this, of course, is quality. Everything sounds like it's being pumped out of a sega genesis.

So really, objectively speaking, the DCS sound board is better at sounding like real music--because it is. But the Pre-DCS soundboard is better at creating larger, longer soundtracks with greater complexity.