I've been using the 16 chanel Multimix on a Dell Inspiron 6000 without any issues until I installed the first set of driver/firmware updates. I reinstalled the CD drivers and all was well again. Recorded my 5 pc band off the floor into HS4 beautifully.
I did run into some issues getting it setup on my desktop - audio crackling - and was losing my mind until I read "jimarter"'s post about setting the DMA buffer sizes - and that solved that problem. Thanks jimarter!!
digitalfuzz: I did run into the problem where the menu would not display the list of inputs when highlighted. For me that was because the setting in Options --> Audio --> Advanced--> Driver Mode was set to WDM/KS when I had the mixer set to use ASIO.
I do find that I need to power off the Multimix before shutting down the PC and don't power back on until the computer has fully booted. I go into the Multimix control panel before launching Sonar HS just to make sure it is working.
Luckily I haven't had to call Alesis because this forum has answered all my questions.