Suboxone saved my life.
It's a hard drug to get off of. You have to taper off.
Not sure an ultimatum is a good idea because 9 out of 10 times, the addict chooses the drug.
If he is honestly trying to taper off slowly, keep in mind that because the receptors in the brain that crave opiates are being replaced with the suboxone, he may experience intense cravings and start using opiates again without suboxone.
On the other hand, it seems from what you've said about Xanax and Adderall, he may not be totally ready to get sober. But if he is, I don't think telling him to quit suboxone all together is the answer.
I understand your frustration though.
Good luck with everything!