Audio Art is an excellent brand, easily the equal of the PPI Art Series that were it's contemporaries. The 400.2XE is a 2 ohm stable amp that should conservative go for 800w into a 4ohm mono load. The XEs had nice built in crossovers that were essentially set up like they were external, as RCA connectors are externally run from the crossover to the amp input.
Selling price would probably be 200-275 in great shape, 175-200 with some typical wear.
I have 2 of the smaller 200.2s available if you wanted to add a couple of more of them to match the 400.2. I'd give you the price that one of them sold for on ebay if interested (I sold 1 of 3 so far and was about to post the other two)
