4. Do you know how long it would take for a 7Mhz 68k to decode an MP3 to an 8bit audio file? And given the lack of FPU... I would suggest days... You like to wait several days with your A2000 doing nothing but decoding an MP3 to a crappy 8bit 20Khz sample just before you can play it?
You probably would prefer using fixed point math (FPU on 68k sucks). You can also (probably) tweak decoding algorithm to go faster at loss of quality.
