360 addon isn't bad, but if you're going to be hooking your player up to a home theater, look for a stand-alone deck. There are sound issues with the 360 player and no fix anywhere in sight.
I don't know about the A20...I haven't read any reviews, but it's supposedly just the A2 with 1080p playback. The A2 can now be had for like $350 on Amazon and the XA2 is around $555. I think the A20 is in the $450 range and seriously, if you're going to spend $450...just spend another hundred and get the XA2.
1080p, analog audio-out (in case your receiver doesn't have HDMI), the Reon VX HQV upconvert chip (which the A2 and A20 do NOT have)...it's worth it.