Loosely speaking contemporary rock from the 70s onwards. Peter Gabriel, frank Zappa, led Zeppelin, sting, Tom petty.
Some rock/blues as well.
Vocals, guitars, piano is important.
So - am I understanding you correctly if I think you say is you might want a colored/mid-centric DAC?
I haven't heard the Questyle, but tend to find most modern DACs to sound quite similar with regrades to sound signature - because - relatively speaking - they are all trying to be neutral. They vary mostly on detail retrieval and speed in the different frequency areas,but they mostly have a quite similar tonal balance.
FWIW - I guess what I am saying is that it is more effective to roll tubes, amps or headphones than a dac if the objective is to alter the sound signature. I'd say - if you have a great deal on a great dac with a neutral sound signature - get it and spend your efforts rolling tubes instead of dacs ;)
That's what I think. It is hard to predict the perfect synergy with dac's. Also, the variation in sound signature is more relevant in less expensive dacs in my experience.
Yes, the best are the `75 then the `74 (SWGP, silver shield/ gray plate) 6N23P Reflektors. Other getter types and years can be good but not near as good as the afore mentioned tubes. There is a thread on HF reviewing some of the best-of-the-best 6DJ8 tubes covering these 6N23P types from a fellow contributor; I will post that info here when I locate it.
For a DAC you absolutely want highly resolving and detailed (with a sense of musicality) on the top of your list of wants. Remember, nothing can bring those sonic attributes back if they're not there originally.
Based on my experience with the WA2 I'd say that sounds like good advice! What you don't want is something that's too dry and analytical, and with the hd800 you're better off to error slightly on the warm side.
Here's a thread started by Rob @rb2013 where he does his 6922 tube shootout:
This comparison should give you some great insight! Don't be afraid to PM him with questions; I also purchased my `75 6N23P tubes from him.
@Franatic recently was also impressed with them in his WA2.