If you are considering XRS, I would suggest HO instead, which would be smaller than the XRS. It gives a bit more bass output than the single driver monitor and has higher sensitivity. It is logical to think that the larger speaker needs a bigger room. My sense is that they are better for a smaller room than singles as they will give more natural frequency response at lower volumes and with less watts.
I am an advocate for the alnicos over the ferrites. I find them richer, more textured, more natural. The highs are fine to my ears; the ferrites have more extended highs.
Regarding subs.... I run SAM HO's with bass reinforcement. With Louis' blessing, I have the ports completely plugged to make sealed cabinets. At a slight cost to bass output, I find the bass to be markedly more articulate. With the subs, the slightly less bass output is no problem whatsoever. The blending is undetectable (may depend some on the subs you have). You can get away with less distance from the front wall more than with rear ports. This doesn't seem to get much response whenever I post about it, so I'm guessing most don't go this route. But I'd be surprised if someone tried ports plugged with subs and preferred ported.