Long story short, we talked a bit... and I helped him choose some tracks for the episode. He wanted stuff of mine, so that's what we went with.
Additionally he asked for title and intermission music. So, I composed some new stuff that evening and sent it off. He liked it, so it's in.
Upshot: eleven of my MIDIs, two of them brand-new, will wind up being featured in the free version of SIGIL. I'm not under an NDA or anything but I do still kind of want to keep the new music and full track order a secret until it's out. :P From what I can tell, the assets for the WAD have now been finalised.
I'll be getting a credit in the text file and a Beast Box in return.
...Needless to say, my flabber has been well and truly gasted.