The 0.8.8 xpra windows client dist has alternate speaker codecs packaged, but the beta 0.9.0 doesn't.
In order to run alternate speaker codecs with a win_client, one has to install 0.8.8 and then install any betas "over the top" in order to incorporate the other speaker codecs.
Good catch!
Fixed in r3036 - please close when tested, new beta uploaded:
$ md5sum Xpra_Setup_0.9.0.exe 7bc66f6b78baa99a1fbfcf347c14e0f9 Xpra_Setup_0.9.0.exe
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/301