It’s true, the visa rules in China are a serious pain. They don’t try to make anything simple, ever.
What you should do is discuss this with your employer, because there are a lot of factors that you’ll have to consider to find the best solution for you. A Z-visa is probably best if you’re going to be working there for an extended period, otherwise an F-visa is always an option. Some info on the different types:
F Visa: as far as I know, you can get a six-month F visa without too much trouble. You might need your employer to convert your L visa to an F, or you can take an invitation letter to Hong Kong and get the visa that way.
Z Visa: your employer will be able to get this for you, it’ll require a medical test in Chengdu and some paperwork. It’s a hassle but fortunately it’s on your employer to go through most of the legwork for this kind of visa.
For more info on China visas, check this out: http://wikitravel.org/en/China#Visas
Hope this helps,
Charlie