Aye, was testing it all out in creative and figured out the non-convertibility thing (which I don't have much of an opinion on). Thanks for the heads-up, though! And for the info on vacuum hoppers in general, as I hadn't used them before. They're pretty neat!
And for any curious parties: it should come as little to no surprise that the brain in a jar does not work with an xp drain. Vacuum hopper would've worked fine anyway, but 'tis a pity nonetheless, as I personally would've found it a bit hilarious.
Also, alas, the dark nexus does not consider the luggage to be a killable entity, and the traveling trunk can't be picked up with its contents normally. You
can pick it up with an entity mover, but I'm having a bit of trouble keeping full movers in the activator and pulling empty ones out of it.