I would almost bet a months wages that you can't use both cards at the same time. Alesis recommends that you disable any other audio cards driver before using their card.
Also, there WILL be some problems with digital clocks not being the same.
I could also potentially see a problem with the actual music being recorded not being in sync with the playback music (I suppose you could fix that after the fact, but what a hassle)
Last I heard, Alesis was not really supporting that card for multi tracking on a PC. They said they were "working on it" but I am not sure that they ever got there, seeings how they have had a hard enough time just getting the card to work in the original way it was intended to, which was to do sample accurate transfers to and from ADAT's and a computer.
You could always try your idea.
Good luck.
Ed