Phone [Q] [i9505] Trouble with Odin and Kies recognizing phone

Hi there, XDA! I'm a long-time lurker and never really found the need to post anything before, but hopefully someone can shed a little light on my situation.

First, this started when I was trying to SIM unlock my phone. After several days, I settled on a post that mentioned downgrading to a 4.2 modem, or ideally full 4.2 firmware. In an attempt to downgrade, I performed a wipe and factory reset on my phone. I've used custom recoeries and roms before and I'm somewhat comfortable with Odin, but this message had me stumped. Whe attempting to flash a custom rom or recovery, I get the message "There is no pit partition" (EDIT: I tried one more time to make sure I had the error message right and flashed TWRP successfully, but get the same message with any roms).

I did a little research and found what should be the appropriate pit file to sort this part out but when I include the pit file in the flash I get the message "Complete(Write) operation failed." Kies also never connects to the phone, although Windows and Odin do fine. Any thoughts?