Best Speakers for a MAC M5200

This is certainly not a new topic question but the others I've read on this haven't exactly been all that informative.  So, I thought I'd start this one.

I'm searching for a good upgrade of my present speakers (original Paradigm Monitor 9 purchased circa 2000).  They still sound great with the MAC but I'd like to kick it up a notch.  I've already done many hours of critical listening but have yet to hear something that makes me want to yank out the old checkbook.  I've heard 4 and 8 ohm nominal load speakers and I'm wondering if this particular MAC really does better with 8 ohm.  It's been bench-tested and proven to deliver 130 watts RMS into 8 ohms and somewhere between 180 to 206 watts RMS into 4 ohms, according to various reviews I've read.  Both MAC Labs and other knowledgeable audiophiles I've consulted have assured me this amp is quite capable of driving a wide variety of good quality 4 ohm speakers without breaking a sweat.  However, being able to drive those speakers and get everything out of them they are designed to deliver is a whole other question.  I'm not an expert on this (far from it) but it seems, to me, this amp does better with 8 ohm speakers, overall.  When auditioning it with 4 ohm speakers, it seems the more efficient or sensitive these are (e.g. 90 dB or better), the better the performance characteristics.  I auditioned it with aggressively discounted 4 ohm nominal load Aerial Acoustics 6T and the sound quality was very impressive.  In many respects, best I've heard, thus far.  However, I thought these Aerial sounded noticeably sweeter, fuller, richer and more musical on the 4 ohm taps of a good high-end tube amp.

As I always have and always will, I will ultimately let my ears be the final judge but I'm wondering if you experts out there who, hopefully, arent' trying to sell me anything can help me save some critical listening time by answering this question. I'm trying to keep this latest upgrade at 4K or under, preferably new but I am willing to consider demos or trade-ins.  I do have to contend with room placement issues.  So, wide speakers like Vandersteen model 2, Klipsch and other wide cabinets are out of the question.  Also, I cannot place the speakers any more than 32" from the wall behind them (32" from wall to front grills).  Finally, because of another room placement issue, I cannot separate my Paradigms by much more than 5.5' apart (from center of bass woofer of left speaker to center of bass woofer of right speaker).  So, here also, slender cabinets would be better in this respect.  The listening room is one end (about a third) of a 23' X 14' open concept style rectangular living room with 9' ceiling.  That one third listening area is approximately 9' X 14'.  Providing a more detailed description than that here would make this post much longer.  So, suffice it to say by way of an example that I've been told the Monitor Audio Silver 300 would probably be a better choice for my room than the Silver 500 and, similarly, the Revel Performa3 F206 better than the F208.  However, I'm not sure about that.  I will likely have to prove that to myself before making my final decision.

So, sock it to me fellow audiophiles!  What do you all think I should be spending my valuable time listening to?