Nice write up, as usual. I know it's insulting to compare my lowly S-25 to your magnificent S-275, except that they really are the same
model, just opposite ends of the bling spectrum. (Which I think suits both of us :tickled_pink
Anyway, I know I've expressed my lack of interest in XR-7s before, and it's just my opinion and all that, but I felt the same way about the sound of my S-25 that you seem to feel about your S-275. That is until I installed HB-1s. Now I love the thing and pick it up as much as any other guitar I own.
Be warned: even thought the S-25 came with HB-1 pickup rings, the routes are not really as big as they should be. I managed to squeeze the pickups in there, but only because I was too lazy to open up the cavities. Next time I have the strings off I'll remove the pickups and shave a little wood with a sharp chisel just so that I can adjust the angle of the HB-1's correctly.