Budget wise to drive my fronts and centers, I would like to stay under $800. I can currently get a B stock XPA-5 for $699, which $100 more than the XPA-3.
If the XPA5 is truly as good, per channel, as the XPA3, it seems like a much better buy. Only $100 more for 2 channels more of the same power.
What monoblocks were you thinking of that actually fit into your budget?
While finally depending on which surrounds you buy, whether PSB or not, and what receiver you currently have, my guess is that would work fine. In fact, all of your solutions work. As far as space, a vertical rack requires minimal footprint. As far as power, if you have just a single dedicated circuit for the HT do I think you are most likely perfectly fine (unless you have a seriously mad, multiple subwoofer setup).
I like the idea of multiple amps. More flexibility. You never know, you may go 7.1 one day. Or 9.1, like I am thinking. Maybe you win the lottery, get a huge room, and go 11.1. If any of the amps have a problem, and needs to be sent in for service, at least you will have some usable channels at your service.
Anyways, I would get the most power that I can for the Maggies. Low impedances, and very low sensitivity.
Which PSB were you thinking of?