Ya tuning high isnt going to make it louder. Tune to your cabins resonant frequency for best results.
Also dont be afraid to make alot of different enclosures and try new things.
As for Stetsom amps i have been using them matched with my DC subs for a while now and had nothing but good luck, burping, bassrace, phyclone, demoing and bumpoing to and from shows. They are strong amps make huge power and you dont need 16 + volts either. I would recommend them to everyone but if everyone used them it would be bad news for me!!! haha