I can vouch for the DB and the AQ as being some good power for the $$...but I know nothing more than what I have read here about the Crescendo..I did talk to a guy here who swapped from a Orion HCCA 2500 to the nendo 3.5k and was disappointed in the sound difference. Don't get me wrong, the same differences probably would have applied to the AQ and Db too...u get what you pay for applies in more ways than one...
Unless you are in stiff SPL competition and need nothing more than raw rms power, look into the specs beyond rms power. Power output is just a starting point. First, all else being equal, 2x power = roughly +3db gain..noticable, for sure, but not a major difference to the ear. It is how CLEAN the power is (THD), and how the amp CONTROLS the power(Dampening Factor) that have as much if not more influence on the perceived sound than simply doubling the power output. Simply swapping one dirty and unbehaved amp for another is really pointless...and this is also the difference between a $750 IA 2.0 and a $430 AQ 2200D
If you can get an IA2.0 for $450, you better jump