[baglunch]

The Dynalo I've been using has been wonderful up until I got my Westone UM3X's, and now my Earsonic SM3's.  With these IEM's there's a quiet, but audible hum that I've never noticed with any other headphones (full size or IEM).  Perhaps my last couple IEM's are just more sensitive than the amp was built for.
 
My music spans the spectrum: classical, pop, metal, folk, country, rap, etc. 
 
I listen portably, but don't want the encumbrance, additional expense, or quality compromises of a portable amp.  Most of my listening is done at my desk at work, so I'd like to find out what a good amp in the $500 and under range would be.  Custom build or OEM, new or used.  Prefer solid state for longevity, (relative) durability, and discreetness of appearance, but if there's a compelling tube amp that I should really know about, please mention it.  I'm prepared to be convinced.
 
Alternatively, any suggestions for further tweaking my setup to remove the hum are welcome, although I am not much of a DIY'er.
 
While I currently am only using my rig with my SM3's, and want an amp that will do them right, I realize I may get some full-size headphones down the road, and so I don't want an IEM-only amp, if there is such a thing.
 
I've been reading good things about the M^3, Caliente, and the upcoming Schiit Asgard (but concerned about that one not being widely reviewed yet).
 
Thanks!