You've got that 100% correct. I drive to places most of the time so I have no need for the battery function, though the flexibility wouldn't hurt. I really don't want to lug around a big amp, or a small amp with a bulky PSU. I'm even open to getting one of those DIY CMoy amps as long as it's good.
Basically I need a HP amp which I can move on a day to day basis, that's the best bang for the buck.
If it's just the NX1 vs the E6 and they're at the same price point where you are, then definitely get the NX1. Throwing in the T30 for just a bit more money seems like a good idea, especially since you have a car, but that isn't the only concern here. Since that isn't designed to be a portable, the chassis besides its size (including the PSU) isn't really designed to be a portable. If you just throw that into your bag for example you're going to need a really good bag to protect it from scuffs. Look at the protrusion on the front panel - that looks nice on a desk but that's a liability on the go in most bags. At a minimum, you'll need to use a camera bag or a cam bag insert, so you can configure it to hold the amp in a single compartment and give it a snug fit. A better option is to use one of those professional cases, but the Otterbox or Pelican that can fit that would probably cost more than the amp. That said, I've seen some set-ups on the Schiit Modi and Magni threads where they get one of the larger cases and then carve out the interior to hold the Schiit gear and a headphone like the HD600.
You can also leave the T30 at work, maybe lock it in your drawer at the end of the day, and just use a different DAC+Amp at home, but of course this can go well over your initially stated budget.
