I'm sure it could be done. It'll be interesting to see what, if anything, Rick does to protect that stuff as far as possible encryption and such. But even if he did *that*, sampling them and getting something MUCH better than the compressed audio now would work, so it probably isn't worth bothering with.
It certainly wouldn't be legal to distribute those new sound files, however.
That said, it sounds like Rick is strongly considering making a backbox upgrade system to let owners of original games upgrade to his CPU and audio (and video?) system, so this may happen in legitimate form. There's no way it'll be as cheap as an upgrade that JUST did sound could be, however, and you'll then be running emulated code on your original machine (which remains to be seen how well that works, but it's possible it's very very good).
--Donnie