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.
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.