Buy two of them!
I have a DB751 in my collection. It's definitely an extraordinary amp if you like huge lows. IMHO it is not particularly flexible; so if you are not into huge lows, then I would look elsewhere. For live performances, I find that huge lows are often problematic. YMMV
The DB751 is big, heavy, and cumbersome by today's standards. It's also fairly expensive.
Another concern is repairability. The DB751 has a FET-based output section. It's likely the required FETs are no longer in production...meaning replacement parts are likely to become increasingly difficult to source. Aguilar may have a bench stock of the required parts. When they are used up, the only option left will be poor quality black market fakes.
I don't have a feel for the DB751's reliability. My impression is the DB750 was unusually prone to failure. I have come across multiple DB750s in the wild and all of them got stuck in standby and had to be sent for repair. Hopefully Aguilar fixed the source of the problem when they designed the DB751.