I was same time typing as Bossobass and he swooped my amp answer. However one recommendation, are you considering at any time soon to turn your HT into a 7.1 system? If so then consider the 7100 or 770 for that side.
With so much amplification to buy (at once) you could also consider delaying bi-amping your stereo system and get away with 2 M-blocks to start. Just leave your jumpers on.

5 (in 5.1) mean…? Yes, Two fronts/center/L/R surround/LFE
6.1 plus one rear surround
7.1 plus two rear surrounds