Schiit tube amplifiers (skipping the Valhalla for now) - there is something fundamental you probably found out from your purchase of the Mjolnir 2 (though I have not heard it, and would still like to). The original tube on these amplifiers is not very good. It's not terrible, but there is nothing particularly exciting about these either. People have frequently replaced the stock with Mullard or Telefunken tubes, or something else that makes sense per the specific sound the person is after. But what you start from is a hybrid amplifier, where a lot of the goodness of the sound comes from the non-tube part of the amplifier.
I found this truth most recently with my Vali 2. It is a really good value in a first listen to a tube. It'll run Grado and planar, both of which the original Vali would have basically died trying to play. And it sounds quite good with any headphone that is not as brutally revealing as the HD800. But I wanted more. So I eventually put in a tube costing the same as the Vali 2. And how much improvement did I get? It was the most crisp, best sound I had ever heard from the setup. But it did not reach the level of my existing higher grade tube amplifiers. Jason does a really excellent job, but you also have to understand the difference between hybrid, SET, OTL, etc.
The Cavalli Audio Liquid Crimson (again, research - not personal experience. I do not own it, so I've not been able to try swapping the tube myself) is similarly a hybrid tube amplifier. And the majority of the goodness is in the amplifier. The stock tube can be replaced, but you're not going to get as much of a jump in sound quality by changing the tube. If you are interested in Cavalli and tubes, your best option is the Liquid Glass. And I don't even know how its architecture can be described. But it supposedly takes on the characteristics of the tube, yet without putting the load and impedance issues directly onto the tube.
And back to the Valhalla 2 - this is an excellent tube amplifier. I would have kept it, if it weren't for some local members pushing the idea of DNA amplifiers. I was able to locate a DNA Sonett for not too much, though still twice the cost of the Valhalla. And it completely changed my perspective on a lot of amplifiers. When I said earlier I wanted more from the Vali 2, it was this amplifier that I had in mind. Versus the Valhalla, it highlighted what for my ears was a small, extra edge in the sound. Listening to the Pink Floyd album Animals, I heard the perception of an aggressive strumming sound at the beginning. I heard, well, nothing from the DNA. It wasn't fat - it wasn't thin. It just presented the sound, to my ears, as it was originally stored on the disc. I hope you get a chance to hear the DNA Stratus, though it too would be difficult to buy, other than used. I eventually sold all my tubes, including the DNA Sonett, and my solid state Cavalli Liquid Carbon, replacing these with my MicroZOTL2. So I hope you get a chance to hear it too. It is like an OTL, but does something, probably not unlike the Glass, to take the load and impedance issues away from the tubes.
Totally understandable. It's incredible how expensive the speaker gear can get! We walked into a room full of DACs ranging from $10k into the 20's or 30's. That's just for a DAC!
