Sacrofago—I empathize. You have a big problem. First, you clearly have very severe sleep apnea. (Severe is anything north of an AHI of 30.) And your treatment, sadly, isn’t working to the point of alleviating your symptoms, so that you can function.
You clearly need more help: first from your sleep lab/docs in treating your OSA more effectively and, perhaps, from other sources, because there’s a possibility of more than one thing going on. Research other sleep disorders such as Idiopathic hypersomnia restless leg syndrome, REM Behavior Disorder and narcolepsy. (Sometimes sleep disorders travel in pairs, or even threes.) ask your sleep lab. Perhaps you need an in lab study.
It IS possible to combine more than one therapy for sleep apnea. Some people use both a dental device AND a PAP machine. (Two of my friends are doing that.) Plus, there are surgical implant possibilities and surgical possibilities, generally. And don’t forget to consider such things as positional therapy, weight loss, treatment of allergies and other life-style interventions.
A friend of mine with an AHI of 120(!) recently underwent a palate expansion procedure to lower his pressure requirements to enable him stay within the air pressure range provided by his RESMED Bi-PAP. (As he aged, he was requiring more pressure than his Bi- PAP could provide.) It worked for him, and he’s been happy with the results.
Also, a residual AHI of 4.8 isn't necessarily optimal. That means that your sleep is still being disrupted almost forty times a night during an 8 hour night! I felt a huge improvement when my residual AHI went from 3.0, to 0.3 with my transition from my gen 8 to gen 10 REMED APAP machines.
The most important thing is: Don’t give up! Healthy sleep is worth the diagnostic and treatment battle! (I’d like to say “journey’, but frankly, mine was more of a “battle.”
Good Luck! And keep us posted on your progress.