I don't use either one, but Roku claims that they will support 5.1 through HDMI.
I've been running Netflix silently on nearly random movies for the past few days whenever I'm home, just to see if I can get the Roku to stall. Not one stall yet. Funny revelation - the Sony stalled so often on Crackle I didn't even know Crackle inserted commercials into the movies until I tried it with the Roku.