I currently have two different headphone amps. The first is a Cary Audio Design HH-1 tube headphone amp with upgraded NOS Telefunken E88CC output tubes. My Burson amp is the Soloist SL. Cables are the Moon Audio Silver Dragon and the headphone extension cable is the Moon Audio Silver Dragon V3 headphone cable.
The headphones I own are the Audeze LCD-X, the Grado RS1e and the Sennheiser HD 650.
Here is how they sound with this set up:
Primary listening is CD and SACD using a Cary CD 306 SACD Profession Version. I mostly listen to 50’s and 60’s Jazz.
Audeze LCD-X: The clear winner here was the Soloist SL. These headphones are extremely resolving and the Solist SL sounded the best when using these headphones. The bass was deeper, the sound staging better and the overall presentation was significantly better. The Soloist SL just did everything a little better than the Cary. I find myself always using the Soloist SL with the Audeze.
Grado RS1e: This was a toss up. These headphones are much brighter than the Audeze and no matter which headphone amp I used I could never pick a clear favorite. Whichever one I was using at the time was always my favorite. I could never pick a clear winner. Both are great amps and both sound great with these cans.
Sennheiser HD 650: The winner here was the Soloist SL. These cans require more power than my other two and even though the HH-1 could deliver the additional power needed the depth of improvement was greater when using the Solist SL.
I could live with either headphone amp but if I had to pick one it would have to be the Burson.