A soundcard might well be a great idea, although AHI (which AFAIR is bundled with OS3.5) should work with the basic Paula chip.
A 68060 is as good as it gets for horsepower - unless we're talking about the PPC version of AHI here - so you'll probably struggle to get better quality.
You might want to try Eyetech, as they used to make an MP3 player cartridge that plugged into your parallel port.
