HA-2 sounds like the better option because it'll save space if the amp and DAC are combined (I'm looking for portable, not a brick). And when you say "run down" do you mean battery life? If so, I don't really have a problem with that as I have a portable charger that I've never found use for.
So having proper tips would equate to the isolation of customs? I just don't want to lose any bass extension because of improper isolation. Only reason I'm not 100% on the customs is because my ear canals aren't done growing yet (and won't be for a while due to my age), so I don't want to need more than 2 refits until I reach that age. I have to go see an audiologist to get their opinion, though.
The proper size tips are going to work just like customs will. They will make that seal and keep the bass from leaking.