The crunch was probably heating up x2o's sub because of clipping. I am pretty sure the power supply transformers in the GP3000DPro are smaller than the ones in the SAZ-3000D.
As for the AQ3500.... Just like the crunch, the FETs are mounted at 90 degrees with the spring clips. I make a living repairing 90 degree mounted mosfet amps.... Thanks to all the factories who mount the FETs at 90 degrees. The AQ3500 may in fact be stronger than either one of these amps but will it last beyond the warranty period is the real question....
All that being said, I personally think, not sure who cares really:
1. If you can only spend $450 or so, then buy the gp3000d pro.
2. If you can spend $700 or so, buy the SAZ-3000D or the AQ3500 depending on if you want your amp to last longer than just past the warranty period. Depending on how much vibration the amp is subjected to, the 90 degree mosfet amp without some upgraded, careful, hand-soldering like we do on them here at dB-r, may only last a couple months before you break the legs off the mosfets, and it's downhill from there and you are looking at $300-$500 repair bills unless you can get the company or dealer or whoever to cover your 90 degree amp under warranty.
Don't come here and say that the gp3000d pro is equivalent to a SAZ-3000D, it's not, in power output, reliability or warranty. You get what you pay for. I don't know why people think there are just 100's of Sundown Fanboys out there.... Most of the people I see recommending the Sundown amps to you guys DO actually have them and have run other gear in the past and are very happy with their equipment and just sharing their enthusiasm for it. Why does that make them a "fanboy"?