Someone else already mentioned it & it was the first amp that came to mind after reading your post. Crown XLS Drivecore II. Single ended & Balanced. With pro connectors on the back of the amp they can be daisy chained to multiple amps. Can be bridged. Built in crossover is pretty cool..as well as the volume control type you are looking for.
I've used them in the past, solid sub amps. Decent mains amp for low sensitivity hard to drive speakers or any speakers for folks on a budget. The amps were popular with home theater enthusiast's. Designed by Harmon & supposedly uses the same tech as one of the $20k Levinson amps..the 523 or 534.. something like that. Could just be urban legend though. Either way it is a solid amp for sub duty & can be found on the used market for even better deals. They can take a lickin' & keep on tickin'.
Obviously as others have mentioned there are a wide assortment of amplifiers that can punish some subwoofers. The Crown is the one I have experience with