So from there, how do I boot, downgrade the EmuNand to 11.2 or 11.1, and run GW.3dsx?
1. You can find an 9.2 ctrtransfer file and do a ctrtransfer on the emuNAND, then find 11.2 update files and use sysupdater to update it to 11.2.
2. Get a new console that does not have B9S that is on 11.2 or less and use a homebrew entrypoint to launch it, OR, downgrade your sysNAND to 11.2 or less, do the test included in uninstalling B9S that tests what your console will be like after uninstalling B9S, and run it from a userland homebrew entrypoint. You won't find any more in depth instructions that than since it is pure madness.
If you figure it out please let us know the results - I'm assuming a brick of some kind, or just a lot of trouble for nothing.
P.S. If you don't have a Gateway red card even if it works all you're going to get is the dragon menu, you won't be able to get into Gateway mode at all.