My SX-1980 is back from the shop and good as new - partially recapped, a few new bits here and there, and back up to spec!
Anyways, I have some testing that I've been putting off. Not anymore.
Here's what I think. The HPM 100's have a distinct signature that is a bit more different from the HPM 150's than I was hoping - still plenty of bass, slightly higher distortion though... Identical mid range sound, slight decrease in very high freq performance that has the most effect on sound signature. They were good to listen too, but I think there are other vintage speakers out there in the same price range that might be better for me. I noticed that the HPM 100's seemed slightly directional, and sounded most different based on where I was in the room and how I faced them. That makes me think they might have a "sweet spot" from which to listen to them. Maybe in a foam room somewhere someone can figure that out...
The Sansui SP-5500x speakers are still very good all around. Slightly lower distortion than the HPM 100's and quite a bit more clear, with better resolution into the deep bass frequencies. Still planning on keeping those things around.
The McIntosh speakers stole the show today. Both the XR-16 and XR-7 have less distortion (more clarity) than the HPM-100 and SP-5500x speakers. They were so clear, I felt like I could hear the singer's teeth chattering and lips closing. Despite being close sizes, the XR-7 (the larger one) sounds much bigger. No surprise there - the XR7 has something like 2x as many active drivers, and a passive one to boot (and weighs 125 lbs/per). There is a bit of phase interference between the active woofers and passive radiator that makes great deep bass imaging, but you have to be across the room before the dephasage evens out. On the other hand, these speakers seem to attenuate less. I go across the house and I still get clear, consistent sound, at a higher level and quality then I expected. The XR-7 sounds very similar to the HPM-150's, but is just a very little bit less boomy. About even in clarity and accuracy. Very close in high frequencies.
You might be wondering, "What does that MQ 102 equalizer do?" A lot apparently. Looking at the power meters, when the bass kicks it, it adds 3-20 db, or 2x-10x the power compared to a channel without the equalizer. Sounds good too.
The XR-16 is great for music and fantastically clear. It is slightly thinner in the bass range than the XR-7 (with the mq 102 equalizer), but slightly better in the medium/midrange clarity and imaging. Interestingly enough, I can equalize the xr-16 to have almost the same bass response as the XR-7's, but not quite. I think that adding a satellite woofer would make it a better "all around" speaker.
Anyways, I'm going to put these speakers all away (hopefully) before my back craps out.