Upgrading preamp. Best for under $1K

Can also try Class A, my preference.

Schiit Audio: Audio Products Designed and Built in Texas and California

Tired of compromise? Kinda crazy when it comes to sound? Then maybe you’re in the mood for Mjolnir 3, a real-deal, 100% Class-A, no-feedback, dual-mono, choke-input, fully-discrete, balanced-differential headphone amp and preamp. It’s by far the most extreme desktop product we’ve ever done.

This is better to my ears than the Schitt Freya+ (owned it before). The Mjolnir is not as good as my Benchmark LA4 and Holo Serene, but it is a really good 2-channel preamp.

I listen to the Mjolnir preamp and a Schitt Aegir amp each night with headphones, but in a 2-channel manner.

Topping Pre90 for less than a grand, great sound

Thanks for the responses! It seems tubes is the way to go for preamp but will it match well with the B&K amp?

It'll depend on the specifics, but should match up extremely well.  You can always experiment with brands and tube types to tailor the sound to your liking.

If you can wield a soldering iron and follow clear concise directions, try this:

You Can Build the PR-102 Stereo Preamplifier Kit - Akitika https://www.akitika.com/PR102.html

If not, the AVA or Schiit units are excellent.

How about this: 

https://www.audiogon.com/listings/lisb69if-audio-by-van-alstine-transcendence-10-rb-preamplifier-tube