The onboard sound is quite decent. It's not the greatest, but the sq is comparable to the SB live. I will be using the FV24's output in my car system, no need to replace it.
I hooked both of them up to my reciever, the sblive digitally, and the FV24 analog.
I played the same 320kbps mp3 on both systems at the same time, and switched between the two inputs on my reciever.
When listening to mp3's, there's no discernable difference between the fv24's output, and the sblive. When listening to dvd's or other high-quality recordings, there's a small difference, but not much.
I'm getting an extigy, but that's for my all digital home setup