Which multichannel amp to buy

Have you considered just adding a 2 channel for the fronts or do you feel you need more power for all 5 channels. Since you have 5.1 and a 7 channel amp have you bi-amped?
If you are looking for more power consider a McIntosh 205 or a Ayre amp as well.

Gemstone Blue Diamond... first as already mentioned revisit whether you even need another amp.

You may wish to consider the Anthem Statement A5. Very transparent, good match for your processor.

NuForce MCH3 or MCH3SE. These are the multi-channel equivalent to their award-winning Ref 9 and Ref 9SE V2 models. www.nuforce.com

Just get a great 2 channel amp and runit from pre-outs if reciever has them and use its internal amp for center and surrounds to save money then see if you still feel the need to upgrade, there are even 3 channel amps so center will be optimized, surrounds can be driven by your reciever with no problem. On a final note I use a Rotel for center and surrounds and it works great (I run Aragon for mains)