Pros: Delivers world-clkass sound from a very wide variety of headphones, and very full-featured
Cons: somewhat expensive and hard to get
The Leben CS300X has made me re-think what's possible from a headphone amp in general, and tube amps in specific. While it has a highly musical, engaging sound, it's not the least bit tubey or syrupy - in fact it's astonishingly neutral and transparent. Due to its being push-pull, and transformer-coupled, it works well with a wide variety of headphones. It drove my LCD-2, DX1000, T1, W1000X, Ed 8, and D7000 all better than I had ever heard before. It's so good I wish I had one in every room.
Looks nice too:
The Leben sounds great with the LCD-2 and T1 - I could very happily live with that combination for a long, long time .
What has struck me about the Leben is that it seems to work well with all the headphones I own - regardless of impedance. But what's been really beguiling me is how great it is with the low-impedance Denons. I've absolutely never heard the Denons sound so good. Not surprisingly, none of my OTL tube amps really did the Denons justice, it would seem. I quite frankly did not think the Denon's could sound this good. The Leben lets them reveal nuance and detail I didn't think was in them.
I did some rolling with the CS300X. I tool out the RCA grey-plate ^BQ5's, and put in JAN-Sylvania black-plates. I also took out the Sylvania 5751's and put in JAN-Hytron triple-mica 5751's. Amazingly, the Leben sounds even better. I knew there was room for some improvement in the tubes I had in there, but these really do take the Leben up another 5-10% in performance. The lower-gain 5751 is definitely the best choice for headphones, since the Leben has LOTS of juice for cans. The 12AX7 might be better for speakers, though.
As some users have reported, I have a very slight buzz on my most sensitive headphones. Can't hear it at all with my LCD-2, Ed 8, HE-5LE, D7000, or T1. Very slight with W1000X. More noticeable with the DX1000, but the DX1000 has revealed very small noises of lots of amps that I couldn't hear any noise with any other headphones. And to be clear - all of the above is with NO music playing - can't hear it at ALL with music playing, with any headphones.
I can't really express how much more I prefer the Leben to the other headphone amps I have. I want to listen to ONLY the Leben. Unfortunately, I can't take it everywhere But when I am at my bedside rig, it's a real treat every night to end my day with some time on the CS300X. It's special.
While it's hard to get in the US, it's worth seeking out, IMO. Very highly recommended!