I'd get a boss LS2 or radial Di to mix the preamps together and send that to a fender rumble 800 or EBS reidmar 502 or other 2 Ohm amp.
Way easier to send that to the house desk or adjust your backline volume.
If you insist on dual amping, for which there is absolutely no reason imo, you could get two hartke or markbass units, or ampeg portaflexes. Anything 250w and up in parallel should be more than loud enough.