Try turning the humidity down a little at a time. Not familiar with the Resmed S9, but I have seen several people on the forum have problems with humidity that is too high or too low. The challenge is finding the level that is just right for you. The RT cannot know the answer to that. I have not used my humidifier for some time, after I realized that my AHI was coming down when I stopped using it. If I am congested I will use some humidification, but normally just the air flow is enough to have me breathing properly within a few breaths.
Try a little Ayr gel in your nose - it will last a little longer than the liquid, and will help the adjustment period. Do keep up the sinus rinses for a little while - maybe another couple of weeks. However, if the pain is not better by then, or it gets worse, give your doc a call.
Diagnosed September 2009, Respironics System One w/ C-flex and humidifier
Aloha nasal pillows
Not a medical professional, just a patient with severe OSA (31) who has done a lot of reading.