Good discussion, and interesting points.

My personal experience about the difference happened about two years ago.

Disclaimer: my dual core music computer was purchased seven years ago, so it's not the latest technology.

I was using my EMU 1820M (fairly high end card), but it was crapping out. Searched the multimedia productions forum (where Mac pops in occasionally with excellent advice), and learned that perhaps some capacitors were failing. Took it apart (had nothing to lose - it didn't work), and found several bad caps. But this isn't my story.

When it was out being fixed, I resorted to the onboard sound. It was simply so terrible, that I gave up on music until the EMU was back in operation.

Now, I'm sure that onboard sound has improved as suggested by several here, and maybe my machine just had a "worse than usual" on board sound chip, but I can assure anyone that there was simply no comparison at all in audio quality.

Glenn