I was under the impression that any decent 2ch stereo amp will always be way better than a mid range AVR when it come to stereo.
Key word is "always", and that's false in this case, not the SA20.. It looks nice, and there are applications where it might be a good choice though there are better values out there. However, Placebo effects may potentially have you believed that HT bypass is worth it, when it is not if you don't know bypass is on.
So just hook up your RX-A1060 FL/FR pre-outs to the analog input of the SA20 that you assigned to HT bypass and you are in business, and enjoy the better sound offered by the great magician named Placebo.
Biamp is this would be a total waste of time. I believe in the theoretical benefits that are not audible in a blind test, but in your case, I don't even see any theoretical benefits.
Another thing that is always a puzzle to me is, why are there so many forum members asking questions about adding an integrating amp to their AVRs? Why wouldn't they simply go for a real separate, a power amp that offers at least 200 WPC, another less will likely be a case of paying more for no noticeable audible benefits, or even a downgrade if one doesn't need the extra power. That's because the internal amps of some brand name AVRs such as D+M and Yamaha's actually have better specs and verified by bench test results.