Dear TDL,
I use a Leben 300 XS. My phone are Grado 1000's. I can't tell you how they sound on one set of cans vs. others. What I can say is that the Leben sounds amazin. Tonal, detailed, sweet. Plenty of punch and drive. I think that is amazing. I use the Phones during the work day, and then when the office is mostly clear in the early evening I power a set of Snell Type E's. What a combo.
I did put a set of Mullard EL--84s in, and replace what came with the unit. I noticed the old glass was worth the money. Remember, you need (2) matched pairs vs. a quad set. (Cheaper in pairs)
Cheers,
bret