You might want to check out Art Audio. I think I read a quick review somewhere about the two, at a show, that made really sweet music. If I can find it, I'll let you know.
I agree with Wayne and Natale. The Art Audio amps that are frequently used by Soliloquy at shows are very powerful tube amps and probably do a better job at controlling the considerable bass capabilities of the 6.3. As a powerful OTL design I would also think the M60 would be an excellent choice, and I think either of these amps would make the 6.3s sing and may provide tighter, cleaner bass than the Cary(also an excellent amp). I've got 5.3s and have had problems dealing with bass in my smallish, square room, and I found plugging the ports with a couple tube socks can help tame the bass in certain situations without changing the character of the mids/highs--just a little tip. Best of luck.
I own 5.3's and have used Unison Research and Antique Sound Labs 845 based single ended amps and got great sound. I would not rule out solid state however.....the Marsh 400 provides an enormous soundstage with a neutral tonal palette. The preamp is also very important with Soliloquy's. I have achieved great sound with the Bat vk 3i and Audible Illusions 3, but the best preamp,no contest,is the First Sound Presence Deluxe. This preamp simply passes more of the signal then any other preamp I have tried, and I have tried many!