plate amps

Not a lot of the DIY crowd around here. A couple that I find interesting is the Rhythmik/GR Research for their servo feedback and Digmoda for the DSP.

I'm a DIY'er and I too highly recommend Rythmik Audio. Brian's a great guy to deal with, he has a wide selection of products, they're reasonably priced, most of them run class AB, and they have all kinds of flexibility/adjustment.

And yes, they do take the load off the main amp/amps. I run a sat/sub system driving the sats full range with a pair of Atma-Sphere MA-1 OTL's. Using a good spl meter and test disc, the Rythmik powered subs are blended in around 50Hz. It's seamless and there's no additional filtering mucking up the purity of the satellites.

If you're running the sats full range, then the sub is not taking the load off the main, hmm, thinking---wait a minute, unless you were running the subs passively off the AtmaSpheres in parallel with the mains, in which case, you would defintiely be taking a big load off the mains, especially as AtmaSpheres like high impedances. Well a little more info I think would be helpful.