I bought the C9 in March last year, and I have used it every single day at least an hour and sometimes like 4 or more hours, variously with an N6ii with A02 board, DX220Max, and DTR1. DTR1 and 1+ are my favorite. C9 is just by far the best thing I have ever heard. I had a WA8 and I was actually never happy with that, it just sounded kind of stilted to me. OK for gentle music but not for anything rock or heavy. C9 is amazing and does it all, and not only that, gives you four genuinely distinct sounds. It's good with anything except really power hungry headphones. I did use it in tube class A about 90% of the time, but the other modes are good, too.