The more I think about it the more I like it. Much easier to cascade, and if one section goes I just loose part of the loading. It shouldn't fail in a runaway fashion. Also, 324's are a tenth the cost of the Burr Brown chips.
The smaller two units have the same heatsink. I'm pretty sure one is big enough for the medium size unit, but I'm going to measure it tomorrow night to be sure. The largest one has a 12x12 lytron double pass coldplate, and I haven't been able to max out it's heat exchanger with residential power.
So, I need an opinion on whether to go with fewer higher power mosfet devices, or more conventional TO247 types. I still need to match them right? If so, I'll just go with the far cheaper 200W devices and inexpensive cement emitter resistors. Thanks!