K10U, first generation, and K10 custom sound different from one another. Both do sound excellent through amp 3. K10 U sound more organic, with a hefty and strong low end. K10 customs, mine are from a year or so ago, have excellent resolution and great detail. Andromeda have more micro details than either with bottom end approaching the K10u but not quite there. Still they have better high end resolution.
My current favorite with the amp 3 is the Beyerdynamic Xelento, with balanced cables, completely smooth and organic, neutral yet not boring, with a full sound. Really well done.
Actually I have yet to hear any earphone that does not work well with the amp3, those that I can run balanced, at any rate. All were fine with the amp1 as well, but the amp3 is just a bit better all around.