Hi, although I'm not at current doing multi-channel (just haven't completed surround and center installation after recent system relocation), I bi-amped my KEF 100C Reference center off my Adcom GFA 7400 amp, with the surrounds on one channel each respectively, with excellent results. The main channels are driven by a highly modified Aragon 3002 300WCP amp. I have found the Adcom to be adequate for the job I use it for, but I think it's most important to have a very transparent and musical amp for the main speakers.
In your situation since you are using a separate amp for mains, use the optimum power on your surround amp for the center, or 100/100WPC. I'm not familiar with your model of surround amp, but I borrowed my son's GFA 555mkII for a time, and found it to be noisy and not as tranparent as the GFA 7400. I think I would be more inclined to stick with your current surround amp, and upgrade your two-channel amp. Best of luck.
Regards,
Dan
In your situation since you are using a separate amp for mains, use the optimum power on your surround amp for the center, or 100/100WPC. I'm not familiar with your model of surround amp, but I borrowed my son's GFA 555mkII for a time, and found it to be noisy and not as tranparent as the GFA 7400. I think I would be more inclined to stick with your current surround amp, and upgrade your two-channel amp. Best of luck.
Regards,
Dan