I had a great 1u rack mount preamp.
I had a cab.
I bought a poweramp. It was big and heavy and fairly deep.
I had three boxes, a preamp that sometimes I didn't need the poweramp with, and a case that the amp and cab went into that would make everything big heavy and cumbersome.
I sold the lot and got a combo that was one lift and fit in the back of the car.
In your case if you're trying to get a bigger rig for not much money - you can pick up the hartke cab... then look for an older head, Ashdown, Trace Elliot, Hartke etc ... they can be had for cheap- there was a Trace AH12-SMX on here for £150 last week... something like that would do you well...
Then plug amp into cab. If you prefer your preamps sound use that into the effects return, or if not use the amp's preamp, or even both! (you've now the choice)