Going from 350Wpc to 550WPC will give you about 2dB more power. I doubt that it would make a significant difference in listenable output unless you have your 801s in a huge room. You might want to add the BAT-PAKs if you don't already have them in. That would make a much bigger audible improvement.
BAT POLL...
CALLING ALL BALANCED AUDIO OWNERS! How many of you wish BAT made more powerful solid state amps. I have their vk-1000 monoblocs and i love them. But i feel need for 500-600 plus watts a side minimum into 8 ohms for my nautilus 801's. Dont get me wrong, the amps are no wimps. But i'd like to try a bigger amp. But where do you find a big amp that is warm detailed (not overly so), crystal clear, and authoritative at the same time? Maybe i'll add 2 more monos and forget about it. What do you think?