$3270+$400 tax per month + living + meals ... those yan yans are not underpaid, they won't get this income in their country. If they want to go to Taiwan, they are welcome to do so.
I also heard that Taiwan offers higher salary than in HK, but it seems they need to pay tax - I'm not sure. My maid (Yan Yan) has worked in Taiwan for 3 years before coming to HK. If Taiwan is so good, she won't come to HK.