I'm interested and can help test initial release. I've been watching this thread for a couple weeks, have 2 Suez models, both still have stock software on them.
Let me know how to get started helping test.
Edit: I went into exact detail.XD
I won't be going into exact detail, but this should get you on the right track if you haven't done it before.
If 100% stock, I would follow the following method for unlocking and installing TWRP in one shot:
https://forum.xda-developers.com/hd8-hd10/orig-development/unlock-fire-hd-10-2017-suez-t3913639/
From there make a backup in TWRP of whatever stock setup you have if needed for later. Then in TWRP wipe system, data, cache and install ("flash") the 14.1 build zip from the start of this thread. Install the recommended google apps from the first post [5th post? arm64 7.1 nano], boot it up and get the basics set up, maybe install an audio streaming app, streaming video app for testing audio.
Headphones, when plugged in, should have no sound at this point.
Reboot to recovery ("TWRP") and make a backup of this minimal installation of LOS14.1 and then flash the headphone fix zip that I send you over PM (or possible it'll be ready to release by then.). If all goes well, you'll have LOS14.1 running on your hd10 with headphones working.
The testing involves trying to break it. Minus the issues that are listed under "Known Issues" in the release page of the fix, you'll be trying all different combinations of plugging it in, unplugging, trying different apps, rebooting with headphones plugged in, unplugging them while playing audio, trying headset with mic, trying normal headphones, trying bluetooth speakers and headsets, turning Bluetooth off while playing audio while having headphones plugged in to see if they fall back to headphones correctly... try to make it do something unexpected. PM me with questions, happy to help.
Bonus would be after that 14.1 testing to wipe system data and cache, then flash LOS 12.1 and do the same. Install recommended google apps, minimally set up, backup then flash the headphone fix and try your best to break it then report back.