how good is the audio?

I am thinking about getting this as a gift for my father for christmas
but I wanted to know how good the audio is first. He would be using
the line in to get a signal from his radio and would be doing DSP type
stuff on it and then outputting it (i hope that makes sense). Is it
possible to use any of those USB audio cards with the beagleboard to
improve the audio quality?

I can't comment on the DAC and ADC on the beagleboard, however it's my feeling that 16-bit audio is pretty much a solved problem these days. Even a cheap onboard sound card has an adequate DAC and ADC section. We're probably not talking pro audio quality, but for recording from the radio, I'd be surprised if the beagleboard isn't up to the task...

What I meant to say is amateur radio, after re-reading what I posted,
I see that it might have come across as FM radio or something. His
current hobby is dealing with building an amateur radio in software
and I was thinking this could be the perfect device for him. I was
able to find the tech specs for the TPS65950 but it turned out to be a
little bit too technical for me.

If the audio quality didnt turn out to be good enough, is it possible
to use USB sound cards with the beagle board?