With isolation and high quality and portability all standing in importance, I wonder if you're open to IEMs? There's really no better isolation solution, in my experience. Some of them also admit balanced wiring. And with your amp you can start off singled ended and try out balanced later on.
You can find some very nice IEMs at or below the $500 mark. Of course you can easily spend more! 
I have a pair of the less expensive etymotic IEM and it did take a while to find the right fit (small tips? large tips? foam tips? large tip on the right and small tip on the left?). But now that these are comfortable for me -- and that took a few weeks -- they are amazing in their versatility and I use them almost everyday, on the bus, when walking etc. Supremely portable. What I learned was that the very high isolation capability really gives a boost to the music when you're in public spaces by closing out so much more external noise. You can really hear and attend to the music you're playing.... and not the conversation in the next seat or the sound of a big diesel engine pulling away from the bus stop.
I don't know the V-Moda's, but there is a lot of experienced members here who use these. I'm sure you'll get lots of info on them.
Edit: And these totally blow the budget, but just as a data point, take a look at Steve Guttenberg's review of the FitEar ToGo 334... which he reviewed based on the ALO Rx MkIII amp. http://news.cnet.com/8301-13645_3-57486297-47/the-best-in-ear-headphone-in-the-world-the-fitear-togo-334/ I can't recommend based on personal experience... but the IEMs are super in isolation, portability... and some of them really hit the sound quality out of the park. Again what I can't tell is whether the musical personality of these things are going to give you the sound 'profile' you prefer.
Edited by flatmap - 10/17/12 at 9:18pm
