software

Well, I tried the series/parallel mod using a push/pull pot with a Hot Rail-- not a bad sound, but now I have hum-- the other humbuckers in the guitar are fine just running off the pot (no mods). Any ideas where I went wrong....?

my guess is a ground is kinda shakey. check all the grounding points and see if one looks weak. hum is almost always a grounding problem

Well, I switched back to a straight wiring for the Hot Rail and used the push/pull pot to simultaneously split an HS-3 and HS-2 in the same guitar that houses the HR... Much better!!! I believe that the Hot Rail may had developed a ground loop problem due to the series/parallel mod-- no big deal as the modification just didn't offer that much. I'm getting a wider array of useful sounds with the new mod.

As for the ground problem, there was no hum in the other pickups, so I'm pretty sure it was a flaw linked to how I wired the Hot Rail to the pot's switching options.