If you've got AA 1.5, I seem to recall that it was not compatable with the Alesis USB/FW mixers...Some driver recognition issue or firmware issue. It's a problem with the mixer, not AA. The Mackie Onyx mixers work fine, as do most other USB/FW devices. However, AA2.0 uses ASIO drivers, and such, should work fine with the ALesis board.
What are you using?