Best amp under $6k, in your opinion?

Regardless of room size, speakers etc - buy used Musician III (about $3k) - send it to Spectron for factory upgrade to Mk2 - $1.5k and for $4.5k total you have one of the best amps in the world.

Problem is that used Musician III is soild within 24 hours.

New Musican III Mk2 retails for $7k - so find a good dealer and press on price and you will get a new for slightly above $6k.

I don't have to describe the amp - do search on Interent or go to Spectron Audio web site for professional reviews. No amp with retail cost below $15k can come even close to this one - midrange of the best tubes amps combine with the iron clad control of the bass

All The Best
Rafael

Hello Perrew, Mk2 is the same Spectron in the sense of the speaker control. There are small improvments, of course - bass is tighter, faster - imaging is sharper.
Where Mk2 shines its the midrange (and highs) - literally SET midrange - many people who own both can tell you the same.
Good Luck
Rafael
P.S. Atm-Sphere is also great amp but only, only if your impedance is never lower then 4 Ohms