Are you using AmigaAmp or Amplifier? I couldn't get Amplifier to work properly, it would play the mp3 but crash after a while, so i got rid of it and got the much better AmigaAmp and used Warp Up mode! :-)
It couldn't also be AHI not configured properly, causing slowdowns, crashing and poor quality. And of course it could be overheating issues as well. I have a Blizzard PPC 160/060@50mhz plus a Blizzardvision and i use a Power Tower to keep this in and i get no problems with heat. Although i am thinking about putting a fan on my Blizzardvision.
What spec Blizzard PPC do you own? My advice, get a tower case and a better PSU!
Regards,