Have you considered looking at a DAC that's already a top performer, but is solid state? I'm thinking something like the Auralic Vega. It has a huge reputation, it's been around a while, and they just came out with a new gen 2 model.
I can say this, as a tube lover, the Vega is the only SS DAC I've been able to use in my system and enjoy. It would make a great foundation to put in some mods especially a nice tubed output. And if the Vega mods go well, you could expand to other models they have, like their digital streamer the Aries (also just came out with a G2 model). Auralic already has a huge, built in customer base that would be good to tap into.