I have played the 3pro (not my favorite amp), but never used a DB359. I have used a lot of tube amps though. I have read on here from other guys that the Aguilar DB359 is not all about clean headroom. Basically it really shines as a low volume amp, but breaks up if you push it.
Volume is tricky when you get into the whole science vs what people hear thing. Watts are watts, but the way tube amps break up, they can seem to be louder than SS amps. It's all about what sound you are going for.
Just a guess, but I would think the two amps might be pretty similar, but I would guess that the Ampeg might seem a little louder in terms of staying clean and giving you a better clean low end.