If you are serious about using frequent flyer miles, I believe you need 60,000 miles on united and it appears to be 50,000 on American (thru cathay pacific).

You can get 20,000 by getting a united credit card if you dont have one and may be able to do the same for american.

There are several other alternatives to consider. If either one of you are over 55, you can join united's www.silverwingsplus.com (which costs $75) and get flights for $660 from the u.s. to china. not bad though tax raises it about $100. (You also need to spend like $25 for a coupon).