I just got the Little Dot MKII for my DT990 600Ω, and I'm amazed at just how much soundstage this thing has when properly amped. I assume it even gets better the more I scale up. For right now I'm just looking for possible upgrades to the stock tubes and eventually maybe a dac as well.
I heard the EF92 Mullard drivers are very good over the Little Dot MKII's stock tubes. What I'm looking mainly for in the driver tubes would be a bass that extends lower and/or is tighter with possibly more impact, and even wider soundstage (can't get enough of it!).
I actually don't mind the treble and the recessed mids too much on the DT990. Power tubes might be an option as well, but from what I understand they don't do as much as driver tubes. I wouldn't mind power tube recommendations as well though.
As for a dac, my main candidate so far is the HRT Music Streamer II, are there any alternatives that are just as good as it that might warmer in signature for around 150usd?