Yes, I saw that you'd asked for recommendation for tube amp and I chose to ignore it, since I had Senns 700, I'd rather have most accurate sound possible, not a distorted/colored one
I think since you already good AVRs in HT and on computer - your best and easiest way is to connect your phones straight to receivers
if your avr can't pull enough volume for your linking (and you're dead set on destroying your hearing) then this amp would be your best bet:
https://www.jdslabs.com/products/35/objective2-headphone-amplifier/