I've been spending the past hour or so messing around with this sampler and the zip-stored sounds included with it. My father has warned me about the dangers of zip disks and drives, so, partially for this reason, I spent most of the time further experimenting with sample dumping.
It turns out that my DPX-1 may very well have been sending samples successfully despite not receiving them, as it appears the problem I had was Elektron's C6 software, which claims to support transferring MIDI sample dumps but really can't receive, apparently, as proven by others' experiences as well as my own.
That being said, I switched to EMXP for sample dumping. While this was first and foremost meant for converting legendary Emu formats (such as the Emaxes and the Emulator II), you can also receive the raw samples from Emax samplers via MIDI, though it appears you cannot transfer samples or sample banks to them at this time. Hopefully its creator will implement that soon, though sending samples with C6 does work, so that will suffice in the meantime.
In short, I finally made my first successful sample dump thanks to a Roland-branded MIDI-to-USB cable and use of dedicated sample receiving software! Expect grainier sounds in some of my future compositions as a result of experimenting with hardware sampling!