it depends on system of 6570 + ram cpu also play major role for video encoding and playback
well wd tv uses 1080p image quality while 6570 give also same if you have good ram + cpu
did you tried both? I mean wdtv and htpc. I build 3 htpcs from last 4 years but image quality is so-so, last one with an p2 x3 720 + 6570 + 3gb ram, mkvs are blurry, blurays looks fine but still feels like software playback, and sound doesn't punch like stand alone bluray/dvd players (xonar dg/realtek alc889). the only idea for better playback is using an ssd drive for system but it will cost too much money.