Hey Kubernetes, thanks for asking. Bottom line? I'm lovin' it!
So far, I've listened at length to the Sennheiser HD-600, the Sony CD-3000, CD-1700, Grado RS-1, and SR-325.
I think the EMP matches up well with all of them. Last night I was listening to some Peggy Lee recordings from the 40s and 50s using the CD1700s. I think they're my favorite for female vocals right now. Her voice is so smooth and sultry coming out of those things.......it's pretty scary how real her voice sounds to me.
The HD600s, as many others have said, do match up extremely well with the EMP. The veil, which I always felt was there with the Senns, is gone. They are utterly transparent now. But the distance is still there. I prefer a more up-front presentation. I hadn't been listening to the CD3000s for quite awhile because I thought they were too bright sounding.....very detailed......but on the bright side. With the EMP, that brightness is tamed considerably. There is no sibilance at all on anything......even on CDs that I know created sibilance before. The Grados also fare well with the EMP.......the bass is particularly wonderful with the 325s, as is the whole frequency spectrum. I have yet to try the HP-1s or the Etymotics.........I'm busy listening to some of my CDs all over again. All in all, I'm extremely happy with this amp. Besides being beautiful to look at (IMHO), the sound it delivers is addicting. For the first time, I know what people are talking about when they use the word "liquid" in describing tube sound. So far, I haven't found any headphones that don't work well out of this thing....................................but I'll keep lookin'.