Welcome inthedeck! Are you going to fess up as to who your brother is, or are you going to leave us in the dark? Or, perhaps I should ask your brother to fess up himself.
I regret I can't help you much with the receivers. I've not heard the HK or the BA, but I believe several members are successfully using the HK with M80s (Mdrew?).
I do have an older Onkyo (TX-DS797) which I've thoroughly enjoyed, and used with the Axioms without incident. However, I used it with the 8 ohm M60s, rather than the 4 ohm M80s. Regardless, I suspect the Onkyo would serve you well.
As for the older woman living below you, your biggest problem will be the bass from the subwoofer. However, my experience with older people leads me to believe that she will be unhappy if she can hear anything at all, even your breathing. this means that if you're really concerned, you shouldn't have any speakers at all and should use headphones at all times.
Again, you are most welcome here.
