Upgrade McCormack or...

I would definitely go with SMcAudio's upgrades.
Pat and Steve provide excellent service, and you can spend whatever you are comfortable spending- though their standard upgrades are probably the way to go.
The nice thing is that they will tailor the upgrade with the equipment you are using.
Though I would ask them for a time frame, if you need the amps upgraded quickly. Sometimes they get a backlog that can keep things from getting upgraded quickly.
BTW, they upgraded my DNA-1's to monoblocks as well as upgrading my Micro Power amps to monoblocks and Micro Line Drive.
All of which perform way beyond their original configuration.

Bob

I concur with Mitch2, 
SMcAudio converted my DNA-1's to monoblocks and also converted a pair of Micro power amps to monoblocks, and upgraded a Micro preamp.
Their work is 1st class.
@soix ,
I would call SMc and provide them with your related equipment. I know it helps if they know what they are dealing with. In every case, Pat has helped direct me during the upgrade path.
Bob

I never heard of Clayton before. I, too, would be interested in the comparison.
B