I use the Solo as dac because of my mic. I basically listen to everything but I like movie soundtracks the most (depends on the mood). I love Frank Sinatra, alt-J, Bon Iver, Woodkid, The Neighbourhood, Nothing But Thieves, 21 Pilots and Elton John (all I could think of).
Edit1: There was a post not long time ago. They said that the tube I listed here sounds almost exactly like FiiO k5 pro.
Edit2: I don’t mind open-back as the market has many variants of them. I also have DT770 as close-back so I would like to expand more into the open-back world. I wouldn’t drastically change anything about my HD600. I only heard that the pads of 6xx/600/650 get worn fast and require annual replacing so I guess I would change that if I could. 650’s sound gets worse if the pads get worn from what I have heard. My ultimate goal is to own different headphones where each one of them has a different purpose. HD600 is for neutral listening and enjoying vocals, DT770 is a close-back that I use if I hear too many people in the house, 650 for warm sound signature and enjoyable listening sessions, etc.