I agree with OP.
Prior Onkyo AVR TX-NR626 sounded darn good, 5.1 and 2 Channel Stereo. (Idle, I needed more HDMI inputs))
Current Sony STR-DN1080 also sounds darn good. 5.1 and 2 Channel Stereo
My small Home Theater, I often use DIRECT, or change from 5.1 to 2 Channel with preferable results.
Inputting 2 Channel content, it would automatically choose 2 channel or I would 'force' it.
Of course your main front speakers need to make good sound, mine are DBX Soundfield 100's with a 10" woofer. Enough Bass for 2 Channel in my situation. Sub is 'in' only for 5.1 video. If it was my main music system, it would be very nice but not outstanding, due primarily to the speakers and space.
http://www.hifi-classic.net/review/dbx-soundfield-100-135.html