Playittwice,
I have KHorns (since 2006) and switched in the last year and a half from McIntosh SS to McIntosh current-issue MC275 VI tube amp and C22 III tube preamp. I don't know how much fiddling you've already done with your system over the years (and I've heard very good things about pairing vintage Sansui and KHorns), but, in my experience, practically every change (from xovers to patch and power cords to CDPs to cartridges to power strips to source material) has made a very noticeable difference in the sound of my system.
I cannot describe completely the change from SS to tube. It's sometimes subtle and sometimes NOT. But I'll say that horns do LOVE tubes; but they also love SS. They are just different relationships. The bass from my 275 is not quite as punchy and tight and slamming as it was with the SS amp (and I miss that a little sometimes), but with tubes, bass is much, much more three-dimensional and has more realism, naturalism, ease, and sustain. Bass is rounder, more complex, nuanced, and subtle. I can sometimes hear the pressure of the pad hitting the skin of the drum now--instead of the seductive, overwhelming SLAM. Also, regarding bass: I used to think it was all about SS tightness and slam vs. tube warmth. Though true, that is just the beginning; and it grossly oversimplifies things.
What these reissue McIntosh tube components did was to give me much more mid-bass (deep voices, woodwinds, standup bass, etc., all of which vibrate my old, wide-plank Jack pine floors). With tubes, I notice the differences not so much in the whomp-and-kick of a bass drum (which has a little less thumb-in-your-chest than with SS), but in EVERYTHING else. Brass is fuller and more fluid and has more dimension and leap and sustain; strings are less strident; voices are more present all around (Johnny Cash vibrates not just the floor, but my bones and chest, and his nasal sound, which used to distract me a little, is as enchanting as a lullaby); choral groups have more distinction among individual voices--as well as air, rise, space, spirit. With SS, voices used to lob dynamically out into the room and pierce like rockets (I loved it!). Now, tubed voices seem to lob out into the room and hang beautifully, to explode and dissolve like starbursts (and I also love it!).
The tube sound with my KHorns is certainly more "transparent" and layered and crystalline than the SS sound, too (transparent: a term I did not ever understand until I added the C22 to the MC275). One last remark: tubes have allowed me to hear all kinds of tiny things and qualities I never knew were there before: the vibrations of guitar strings, the extremely subtle shifts of a voice (tubed Billie Holiday is haunting to the point of tragic). All of that said: It could have more to do with my replacing vintage SS with new tubes. Also: you would certainly appreciate but you may not prefer the sound of tubes.
One difference I now notice is that, with so much more distinction and subtlety, some hard rock songs (reproduced on the KHorns at concert-level volume) have a little less SS harsh in-your-faceness with tubes--less attack. Remembering my younger days going to live rock concerts: my old SS separates and KHorns produced a beautiful distortion (go figure...) that was very close to the dynamic assault of a live ear-ringing performance. Whereas tubes make some of those same bands and songs almost too beautiful and melodic to believe. And I'm not sure which is truer to the original. Basically, tubes have their own voice, which emphasizes certain qualities over others. It comes down to taste. I'm very aware that with KHorns, different tube components sound different; just as different SS components do--even from the same company. I learned this auditioning different McIntosh components, new and vintage, SS and tube, with KHorns. Although I doubt that I'll ever go back to SS with Klipsch, my advice is: get both tubes AND SS.
