Have you installed delfinampeg.device? It allows playback of mpeg audio with virtually no CPU time. Great stuff! It outperforms my Athlon 500MHz Windoze box in terms of playback consistency: No jumps, skips, etc. Do a search for 'delfina' on Aminet to find it.
What version of delfina.library are you using? I found that the older official releases crashed every 3 minutes and the newer releases for the Flipper don't work with my Delfina Lite. It sounds like you've had better luck than me :-)
Enjoy your Delfina!