I have several diy 18s myself (but built my own sealed cabs) and use Crown XLS1500s (current equivalent is the 1502) and miniDSP (2x4) as these amps don't have onboard dsp and originally got them for mains duties, the diy subs came along later. They used to cost a fair amount less than they do currently, too, think I paid in the range of $300-330 each for mine. I do run two subs off each, too. I don't have a literal equipment rack, but rather stands with shelves that hold my avrs and other gear, too....or they can just go on the floor behind the sub. You could put a plate amp on the diy, too....not sure if GSG offers a custom cutout or if you have do your own, but I already had the amps before I built the subs, altho I did get a few more after I built the subs. The Crown XLS (Drive Core series, as there was another/different series years back from Crown also designated XLS) are very quiet amps even though they have fans, the Behringers are known to be a bit noisy so many mod the fans (altho in an equipment closet that wouldn't be an issue).