I recently had a follow up sleep study.  4 hours without CPAP, 4 hours with.  I registered 0 minutes stage 3/4 sleep.  That's zero minutes both with and without.  I managed a total of 7 minutes REM  with my CPAP.  I wish there were a way at home to see if this actually entrains my brainwaves into the delta range.  If there's anyone reading this that has any suggestions, I'm all ears.  I haven't woken up refreshed in years.  In a study with rats, all subjects DIED  between 3 and 4 weeks when denied stage 3 sleep.  No wonder I feel like I'm dying.
Check out herbst sleep appliances -- far less disruptive than CPAP. Not sure where you live but these guys are great: https://www.koalasleepcenters.com/
Tod Tepfenhart