deal with the CU first. the main business all large banks is to shaft customers. you will probably pay a fee for a conversion, then get a conversion rate.

banks are required to post funds from us checks is some number of days. i'm pretty certain there are no such regs for foreign checks. in most cases, foreign banks are better at converting foreign currency and then issuing us dollars than us banks converting foreign currency to us dollars. if we're talking real money here, it may be worth it to get it converted in hongkong bank, and wired to usa.

i presume there are more than one hongkong banks in usa. try contacting them for the transaction.