Well, I can't speak for the Roku, but wiith the Squeezebox, a TV display is quite doable. Not TV-out from the device, of course, but it'd be pretty easy to cook up something that runs on a networked PC and connects to the player to find out what's playing, song position, etc. and displays it on a TV. Likewise, a UI for browsing and selecting music wouldn't be too tough, especially since the slim server is written entirely in Perl, so stealing their routines for browsing/searching the music library should be a snap.

Of course, this all assumes you can spend some time hacking, and won't be as pretty as if the device had TV-out built in (no visuals, etc.) but with a little work, could end up looking pretty nice.