My TENS has a mode called IFC, it stands for interferential current. You must place electrodes in an X pattern, with the channels alternating between top L to bottom R, and vice versa. I can't say that affects apnea either good or bad, as my ASV machine has apnea well controlled already. It does affect comfort though at the beginning of sleep time.
As for purchasing accessories, I just have a wish list until I've got income again.
FWIW any effort to make sleeping better is well worth the results. Lots on this site, myself included, have had to trial and error until things start falling into place IMO. There's several things we can work on with you. Pressure optimization and Sleepyhead Chart viewing is just one thing. After progression, you may find another machine is better. Docs and insurance require us to fully expend all options with xPap we've got before transitioning though.
Hope things begin to get better.