Ah FR/FR = flat response/full ferq range, gotcha.
So if you put an ADA GCS-3 cab sim (or similar) in the MP1 loop, that would work (as MikeB does when he plugs into my studio monitors). But it will need a cab sim or sound wayyy toppy.
IIRC GuitarBuilder uses a pair of full range peavy (small) PA cabs (passive boxes so needs stereo poweramp) with his MP2 and wouldn't have it any other way. But he uses the Cab sim outs on the MP2 (as do I direct to my studio monitors (which are more FR/FR than most PA boxes).
From the link you sent (and for only $169) it should work fine but is mono!!. They look like decent boxes and the mixer/amp should be transparent (but is mono!!).
For what your thinking of, I'd use them like monitors on stage (front line facing back, tweeters hard L/R) which will make FOH mix easier for your sound guy.
I'm happy with cab sim into studio, on stage I still prefer cranked guitar cabs
but man $169 is a pretty good deal (again though is mono so you could buy 2 and run in stereo
). Another way to go with this idea is with powered monitors, but the cheaper ones are pretty chinsy and you'd get better guitar sounds the normal way. I've got a pair of Carvin LM 15 350w powered PA boxes (for PA), they're ok but I wouldn't use them in place of guitar cabs (my 2 cents worth)