I run a Nine.1, and at one point, had a Nine.4 in my car too. They are great bang for the buck amps. My only complaints are lack of ability to completely disable the xover and ssf on the Nine.1. This isn't a really big deal though, cuz you can just set them to their highest (for xover) and lowest (for ssf) settings.
SQ wise, they don't sound quite as warm as an oldschool american made amp would (such as my soundstream D200II). But are very good performers for the money.
My roomate is running my old Nine.4 bridged to a pair of 6500s, gains set to feed approx 175 wrms to comps, and it absolutely wangs, midbass from hell. He's also got a Nine.1 running a 13Ov2 just like me, and it pounds hard just like my car. The Nine.1 is an absolute beast IMO.
Oh, and the 3 year warranty is nice too.