I'm unsure of the exact specs of the onkyo speaker set you said your friend purchased. With that said, I believe each may be rated at 6ohms.
The Sony strdh520 requires 8ohms. I have one, I got what I paid for. The eq consists of bass and treble. Despite its shortcomings, I'm content with it for now. I simply purchased it to test 7.1 at an entry level.
I initially had a few 6ohm speakers connected while I pieced together my speaker set and had 0 problems. I also never cranked it passed 50% until I had more suitable speakers.