As said above, you can get legally into china without guide via a travel agency in China. I can give you there contact info if you email me. You can enter and exit via the kkh or to Tajiikistan. They actually put limitation on where you can go around in China. It is not that anybody will stop you. Nobody cares and the polie is very kind. But if you get into trouble like driving around in a militaria area the travel agency is in trouble, because you are their responsibility. That is why most of the agencies will never let you go without guide. Just stick to the bigger roads and there is no problem. But tell the agency what you plans are. It would be very inconveniënt if we get these friendly people into trouble be helping us.
And by the way, China is great to travel on motorcycle. But very big! It took me 3 weeks to drive on my Chang Jiang from Shanghai to Kashgar. But there are none of those tipical hotels and campings where a lot of land travellers go to, and almost nobody understands english. I studied Chinese in Shanghai fot 2 months before I left on my trip.
Now I am in Istanbul with my Chang Jiang, I have driven about 13.500km now! Ofcourse some engine (burned valves), gearbox (broken gears) and eletric trouble during the trip, but those are the things that make it a bit more interesting.
I will be back in Holland in a couple of weeks. When I am back I will try to find other border crossing for enter-exit into China to make it more easy to cross china with you own bike/car.

For more info on my Shanghai - holland trip see: www.cjroel.nl
For more info on enter China: Email me, see website.

Greetings,
Roel Hendrickx