Most of this info was provided by Ronald Olsen.
Posting parcels to and from anywhere in China is easy. I decribe here how you post thingsa from places in China to Beijing. But it also works the other way round. Most post offices will want you to write the address in Chinese characters, but you may show it to them in pinyin, and they will be helpful. The one thing the post will require now is to actually SEE the object or a portion of it before it is completely enclosed. For these items, ask your hotel staff to round up some cardboard. Mail your parcel to Beijing, to be picked up later. Even fast mail service inside China is not too expensive. Ducttape is good to have. Be aware that some post offices will receive packages, but you can't post them from there. The most notable example of this is Daban.
The address of the international post office in Beijing:
Guo Ji You Dian Ju
Jian Guo Men
Literally, "The International Post Office at Jian Gou Men, Beijing". This is near the friendship store, embassy area, specifically 200 meters due north of the northeast exit of the Jian Guo Men subway stop in Beijing. They are reliable! Just remember to keep the mailing receipt ! Also make sure to ask how long it will take to arrive when you send it. Some helpful Chinese words here, "duoshao tian man/kuai dao Beijing ?" - means "How many days slow/fast (mail) to Beijing ?".
It also works to mail from Beijing to other countries, but that is a lot more expensive, and you may run into trouble with the customs in your home country.