There are airflow sensors, and possibly some other types of sensors inside the machine. Any kind of sterilizing chemical you force into the air path may damage these sensors.
There's a real good chance that heat would damage the machine as well.
You might find a DME who will be willing to take your money and claim he "sanitized" your machine, but I doubt he'll do more than change the filters and clean off the outside with an alcohol wipe. Then he'll probably overcharge you for a new tank and hose. Plus a high service charge and, of course, a hefty markup on the filters. The one thing he might know how to do is disassemble the humidifier and clean those parts, but you can probably figure that out yourself. If you're lucky, he'll be able to figure out how to correctly reassemble anything he disassembles. He may very well tell you that humidifiers can't be cleaned and must be replaced.
Replace the filters, and clean the water tank. Let the machine run for at least half an hour in a clean, dry area. If there's a smell when you put it on, turn the machine on and let it run 10 or 15 seconds before you mask up for the first week or so.
A spare water tank is a good thing to have anyway. Get the S9 dishwashable tank so you'll have a spare. Open up the used water tank. Even the non-cleanable water tank on S9 is openable with some effort. Once you have the used tank open, clean it thoroughly. If you want to go further, boil a pot of water and turn off the heat. Drop the tank in the water for 5 minutes or so. If it survives, it will reasonably germ free. If it is damaged by the heat, use the replacement tank you just bought. I've done this with a PRS1 tank.
However, remember that even boiling water doesn't completely sterilize things. There are some germ that can survive boiling. Most of the nasty bugs will be killed by boiling, though.
I've also used vodka or Everclear (pure grain alcohol/ethanol) on similar parts as well. I figure if you can survive drinking it, having a small amount of ethanol residue left behind is not going to cause a health problem. Everclear is highly flammable, and vodka is somewhat flammable, so be careful. I rinse with water after the ethanol treatment.
I've done the hot water treatment on hoses as well, but I probably wouldn't try that if it's a heated hose. I was prepared to simply throw the hose away if it couldn't stand the heat.
There are bacteria filters you can put between the water tank and the hose. Our host sells these, but I'm not sure they'll fit on the air outlet of the S9 machine due to the tab on the back of the machine. http://www.cpap.com/productpage/Respiro ... -pack.html
I personally wouldn't worry about there being harmful microorganisms in the machine itself. The room air you breathe isn't sterile, either. The inside of the machine is clean, dry, plastic behind some air filters, not some sort of organic material that provides food for germs to feed on. I might worry about something nasty being in the hose. I'm not that worried about the water tank, but I'd clean it really thoroughly anyway.
I found some removable parts in the used PRS1 humidifier I bought and cleaned them thoroughly. I think I just cleaned them in the dishwasher, but I may have given them the hot water dunk, too. I don't know if there are removable cleanable parts in the S9 humidifier.
I do get a laugh out of some of the CPAP ads in Craigslist. They often claim the machine has been "completely sanitized." Yeah, right.