Since you mentioned Aune, I suggest you look into the Little Dot amps and see if any of them is a worthy candidate. They offer tube, hybrid and SS headphone amps. Their products are well-reviewed.
About 3 years ago, I got a Little Dot MKIII tube amp for my HD600. It sounds decent, responds to tube rolling and is definitely a good value. I still have it.
About 3 years ago, I got a Little Dot MKIII tube amp for my HD600. It sounds decent, responds to tube rolling and is definitely a good value. I still have it.