Miguel, I'm glad you like your UHA-6S, too! You are right when you say that the Ety ER-4 sounds good with the Leckerton. I've found that, as well. The Shure SE530 doesn't work so well with the Leckerton (that was a surprise, frankly). So, my amps of choice (the one's I own, anyway) are as follows: Leckerton UHA-6S + ER-4S; Mini3 + SE530.
I did notice the UHA-6S does provide a slightly grainy upper midrange when paired with a high-end digital source (my Marantz 8260 CD player), but it's not objectionable at all. When used with my iRiver H140, it's pretty nice!
As an aside, I don't know what all the fuss about the Sony D-25S is. I bought one (not cheap), and I frankly don't care for it. Using either of my amps, my iPod Classic, through the LOD, sounds waaaaaay better - cleaner highs (by far), and there is no upper midrange glare, which is a characteristic of my D-25S that I find troubling. It is a nicely made piece, though!
Cheers!!!