I personally think that there is very little chance for bacteria and or viruses to grow inside your CPAP machine because of the dry environment. Nevertheless, its conceivable that a really hardy microbial strain would be able to survive. I use a S-9 Elite CPAP machine and a H5i Humidifier. My CPAP machine, like yours, does not disassemble for cleaning so I share your concerns about strange microbes lurking in my equipment. I do what I can, therefore, to mitigate the possibility and to lessen my anxieties in the matter. Here is what I do:
After cleaning, I use a germicidal solution once per week to soak and disinfect my mask, tubing, and ancillary equipment. In conjunction with this process, I dampen a clean dry cloth in this germicidal solution and wipe the outside of the CPAP machine, and, the inside and outside of the humidifier. With respect to the inside of my CPAP machine, I wipe the intake and outtake airways as far as I can reach into them. In addition, I change the white filter once per month whether its soiled or not. I also use a room air filtering machine, which I keep running 12-14 hours a day. I find this machine removes much of the particulates and pollutants in my bedroom, which is relatively dust free. This is all I can do but it gives me some "peace of mind".
I obtain my germicide solution from a local surgical supply store but it can also be obtained from one of the CPAP commercial web sites.
I hope you find these comments useful.