I think you should count yourself lucky that sound works at all. Nobody has even looked at the sound code yet, aside from turning it on and off. Everything's been focused on the graphics emulation so far.
The sound frequency is currently 12000Hz (it needs to be evenly divisible by 4x the framerate), but I think we could bump it to 24000Hz (at least) without a problem.
Before enabling sound, I was going to start using C68K, because it'll give us more CPU time to burn on it. I'm going to work on that today, and maybe work on sound a little. I didn't realize that we might have enough spare time to start doing sound already.
Frameskipping will do pretty much nothing at this stage. I might put the auto framerate control that I did for the software version of GP/DC, so it'll automatically skip the occasional frame if it's running too slowly.