So, after fruitlessly attempting all of this with my Windows 8.1 laptop (the fruitless part has to do with the not being able to figure out how to achieve a fastboot-compatible HTC driver under 8.1), I booted a live USB drive of the latest Linux Mint and was able to achieve what I think is S-Off.
Just to be specific, I came to
this ROM from last year's Global leak after first updating the firmware (radios and hboot) to the latest model. I do not know whether the kernel that comes with that ROM is secure or not.
Under Mint, I downloaded and installed the adb and fastboot executables. I then downloaded the rumrunner tgz file and extracted the files in it.
Finally I fired up the rumrunner executable. It went through several procedures, then on the last step, it showed dots progressing for an hour and a half. I happened to get a text msg notification, so took a look and noticed that the USB device no longer showed as being mounted in the notification area. I ctrl-c'd out of the procedure, powered off my phone, re-booted to the bootloader, and saw the magic s-off word in the hboot header. I think that that means success.
Thanks for letting us all know about this avenue of getting to S-Off. It's clear that the Rezound will not be getting any more updates from HTC or Verizon, and having the flexibility to be able to go back to the RUUs is a big, big plus as developers work to keep our phones current.
cheers,
john