Upgrading preamp. Best for under $1K

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

Can also try Class A, my preference.

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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.