There's not much info around on the Sharp 21U (a co-worker bought one recently but I don't think he's unboxed it because he's searching for the cheapest player he can find and things that he may return it for a better deal). The 50U will decode everything except DTS-HD Master Audio and has a 5.1 analog output. The 20U will decode DD+ and TrueHD only (with a 48kHz/24bit hardware limitation) and has a 5.1 analog output, but it's a Profile 1.0 player and I don't recommend any of the players released prior to last fall (when Profile 1.1 support became mandatory).

This thread at AVS offers a great overview of audio support from different Blu-ray players. You'll notice that there are a few different players with onboard decoding and 5.1 or 7.1 analog output (Samsung 2500, Pioneer Elite 05FD, Marantz 8002), but the prices tend to be higher for that capability.