PREAMPLIFIER UPGRADE QUESTION

Great selections but I'm biased to the Balanced Audio Technology sound. Have a look at BAT VK-80 over at music direct. It hits the budget you gave

Buy the Zesto.... you can thank me later !

I bought a used Ayre Acoustics KX-5 Twenty preamp for just over $5K.  Fully balanced and dead quiet, it is very dynamic at lower volume settings.  I can't believe what I was missing before.  I've got it paired up with a Parasound JC-5 amplifier pushing a pair of Infinity Kappa 9's.  There's a lot out there to choose from because many people are dumping expensive preamps in favor of bypassing and using a DAC with a volume control.  I'm not in that camp, get a good preamp like the KX-5 Twenty you won't regret it. 

If you love your Martin Logans look for something that plays well with your electrostatic speakers.  I had McIntosh and it did not work out very well sent direction I had to go in a differ 

Good Luck and let us know how you make out!

As per some that have suggested something that does not need be pricey to be excellent, what you’re describing really does fall into the camp of SPL. Yes, I’m a fanboy of SPL. But the Elector pre had literally transformed my system. The newest iteration has additional outputs for both balanced and single ended, but it is a balanced preamp with exceptionally low noise floor and true to source. Also with an astounding stage, placement accuracy, realism and clarity. Very little coloration, but still maintains a bit of tube like shimmer. 
 

Many have used it with much, much more expensive systems without it becoming in any way a bottleneck or mismatch.