One thing nobody has mentioned yet is the difference how the Amiga played audio and how modern systems do it. Modern systems interpolate samples to get different notes then play this at a fixed rate (44, 48, 96KHz etc).
The Amiga didn't do this, it played the samples at different rates.
This is an important thing to consider because the low sample rates Amiga apps used generated a lot of quantisation noise and this was of course part of the Amiga's sound.
If you try and interpolate samples up to a higher fixed rate you'll lose this sound. If you are upsampling (as seems to be the case) the number of sample you add per sample will be different for each rate, this means you'll be adding quantisation noise but in a different way. Many of these frequencies will above human hearing range but not all.
So, in short if you're not careful you could end up with 8 bit Amiga audio sounding very strange. I guess it depends on how accurate you want it but if you want high accuracy you'll need 2 different systems.
--
BTW why are you using a 68K processor? Wouldn't it be better to use a PPC, that way you can emulate the 68K and you'd have a faster processor. It also gives you at least the possibility of running the likes of MorphOS* (assuming you could talk them into supporting it).
*I'm not saying OS4 because it's in legal limbo and will probably remain there.
