Hum noise is always a risk with external amps. I think all my external amps (including ATI) had hum when I was living at my previous house. I had to use a cheater-plug (which you're not supposed to do
).
I think the RX-A2060 can already power 5.1.4 just fine (to loud volume) since it was made for 5.1.4.
Those 4 little ceiling speakers don't require much power anyway, probably 1-10 watts.
Just set all speakers to small and let the subwoofer do all the heavy lifting (GEICO commercial: it's what they do). Then your 5 bed-speakers will require about 1-50 watts. It's what they do.
So I would use A2060 and save up money in your HT piggy bank.