Unfortunately, the Multimix USB only streams the 2 channel audio from the Main Outs, not the individual channels. Alesis says on their website, if you want to use an ASIO driver to download ASIO4All. This is very lame for a manufacturer to not write their own driver for an interface. And to think this s Alesis coming up short.
Your best bet is to find another interface, one with its own ASIO driver.
sorry, but hope this helps.