Amp Upgrade time, $6000 budget, used or new.

Amp upgrade time!!! What’s the most badass amp I can get for $6000 New or used. 
I’m currently bi amping my Martin Logan’s with an old mc7106. I want to move up. I’m not glued to biamping this time around, I just do it now because my gear is my gear, ya know? 

I would like fully balanced. 
So please help me pick my next big boy amp. 
Treated room. Speaker:
martin Logan esl x , rel t7i pair 
Preamp:
 t+a P3000hv
dac / phono
t+a DAC 8 DSD / nova phenomena 2+
streamer, tuner, Tt
metrum Ambre , marantz 20b, marantz tt15s1 
ic and power
synergistic.