What Is Best Monoblocks For Around $10,000 Used?

I second the Lamms. I don't think they can be beat in this price range. You don't mention power restrictions, though the amps you've mentioned do have more power than the Lamms, but lack the Lamm's sonic refinement. If you can get by with a mere 200 wpc, check out a pair of Lamm 2.2's.

Dark sound usually suggests that the highs are slightly rolled off.

You need to hear the Pass Labs X600 mono blocks. The bass is exceptional and the amps pull in detail in the entire range. You can find them used for around $7500. I have absolutely no desire to trade, upgrade or sell mine. They're that good!

I didn't specify a power requirement, since as I mentioned, I will eventually be upgrading the speakers. If I can find a pair of outstanding amps in the lower power range (>200wpc), then I must search out more efficient speakers (Wilson, etc). That is why I'm seeking an amp upgrade first. Either way, the amp should have enough "beef" to satisfy the needs of my large 8000 cubic foot room.

I could be way off base here but me; I would be looking for a great 2ch pre amp,first.

I highly recommend the Levinson 436 amps. See my ad on Audiogon.
http://cls.audiogon.com/cgi-bin/cls.pl?
ampstran&1136401085
I've used them for several years and compared them to Krell monos, Classe, and several others. In my system (all Levinson and Revel) they have been magnificent. I can provide pictures on request. I have given this advice to many even before I've decided to upgrade to 33s. These amps do some phenomanal things and in the right system can really bring it to the next level. How do they sound? Well they are chameleon like, in that they don't have a sound of their own, but reflect the surrounding cables, sources, and components. Highly nuetral and have let me know the right or wrongess of ever tweak or upgrade I've ever tried. Revealing but very musical, and unfatigueing.
I'd be happy to talk with you, and my phone number is included with my ad.