I have an old sound mod for UH-1H wich works fine in Saved Games, I think it's same structure for your mod. I haven't the BF-109 so I can't test it. Do you use OvGME (more easy to install/uninstall) ? May be I can make it compatible (not sure)
Yes, NP software is absolutely necessary to use it as "real" TrackIR, that's not a true problem, I own the wireless clip and its quality is really better than original one, a friend own the package and he has no problem whith it.
Mods go in ....Saved Games\DCS version\Mods\tech, if the two last folders don't exist you have to create them manualy (Don't forget to erase the mod from DCS core)
For Upuaut Mod https://my.hidrive.com/share/lwer0.o024#$/
For rato65 (link for mod included) https://www.digitalcombatsimulator.com/en/files/3314170/
BUT !!! you have to merge these three mod to use them together (I made it with Eight Ball help, think I can give link in PM)
As Neo 47 answer, all aircraft mods go in .....\Saved Game\DCS version\Mods\aircraft, you have to create manually these two folders, respecting spelling (don't forget to erase first (bad) installation).