Originally Posted by
sdsearch
However, to answer your posed question, as friedablass pointed out, you can transfer MR to Marriott Bonvoy, and then transfer Marriott Bonvoy to AA or UA. Of course, doing a two-transfer may not always give quite as good a value as a one-step transfer, but it is possible.
I would personally never advocate doing AMEX MR >Marriott Bonvoy>AA as that is a terrible value - 60k MR will ultimately become 25k AA so your are losing more than 50% value. There was recently a 30% bonus for Marriott transfers but that still meant 46k+ MR = 60K Bonvoy = 25k AA, still almost 50% loss of value on your MR. To me anything less than 1:1 is no good.
I was answering to the statement that AA had no transfer partner and was pointing out that you can transfer Bonvoy to AA. But I'd only do that with my existing Bonvoy points balance.