Good advice. This should be possible because Rythmik uses a true delay and not a phase control. As long as you don't need more than 16ms of delay and 1 PEQ band you should be good.Than, two subs that are the closest to MLP with a Y-splitter. Than measure with those two, to play with Phase control to adjust for the small difference of distance between the two. Once you got your first two subs perfectly, connect the third one into the second sub output and let your AVR take care of the rest.
Those are the simple instructions, without using tools like REW and MiniDSP, that would give you a lot more options.