I will eventually replace the Kara F preamp with a second Benchmark HPA4 preamp. I tried it on the setup, and it improves the sound a lot, but the $800 Kara F preamp is good enough for a few more years (a bit of faint praise).
I also tried the Schitt Mjolnir v3 preamp. This is a better preamp than the Freya+ and warm sonically and to the touch (actually Class A hot). The Kara F is more convenient since it has a remote.
BTW - the Wotan amp took 30 days of very hard playing before some top end hardness went away. Now it is totally fatigue free and a keeper.