Lunar and Ignition are the only two big ones (US firms) I know of here.
When deciding where to set up a consultancy in China there is one big thing to keep in mind:
What is your target market. If you are designing for products to be shipped to the rest of the world you would set up in Hong Kong. If you are trying to design products for the China market you would set up in the Yellow River Delta (Shanghai, Wuxi, etc.). Why? Because that is where those types of manufacturers are.
The Pearl River Delta (near Hong Kong) is mostly a bunch of Hong Kong companies with factories to export product out of China. They don’t seem to understand how to distribute systems within China. Yellow River Delta has the Chinese owned manufacturers that produce mostly domestic product.