My guess would be look at what Windows 8 is doing - is the Alesis driver Win8 compatible?
Does the Alesis software come with some sort of 'control panel' to allow you to adjust things like the sample rate - this would be a good way to see if things are working properly with the mixer/driver.
I would doubt that it would be an issue with Au as it just works with whatever is presented to it by the OS
Edit: I assume that you have only plugged the PC into only one of the firewire and not both?
Since you are using the Alesis ASIO drivers then the operating system shouldn't have any bearing on the connection of audio through to Audition. Also in the Multitrack view you can see other Alesis line inputs apart from the default Line 1 and 2. So Audition is recognising some info from the Alesis drivers. But I think that the Sample Rate setting of '0' is probably significant.
I would have a look in the Alesis ASIO Control Panel at the Clock Master Mix section and make sure that the Multimix is selected as the Master Clock and not something else.
It's probably nothing but this is from the Windows Dev Center
"In Windows Vista, Windows Server 2003, Windows XP, Windows 2000, Windows Millennium Edition (Me), and Windows 98, audio drivers conform to the Windows Driver Model (WDM) and make use of the kernel streaming (KS) components, which operate in kernel mode and are part of the operating system."
I don't see any mention of Windows 8 - maybe nothing?
Just a thought - why not try the asio4all driver just to see if it makes a difference?
You can install it and then select that driver in Audition - you can always switch back
You shouldn't be using the WDM drivers since these depend on the Windows operating system for sending audio through to audio software like Audition.
Have got the latest Alesis firmware and drivers installed for Windows 7. I would have thought that they should still have worked with Win 8.
Maybe this thread on the Alesis forums might help getting it sorted. There is a similar image to your first one in your last but one message that shows no sample rate and the unlocked warning icons. I think you need to get the sample rate sorted there before Audition will be able to use the Multimix successfully.
Thanks RyClark for attaching the link to the Alesis Community Forum because someone on that forum suggested to try something which I did and It worked.
I managed to get the multimix firewire mixer to work with windows 8. I updated the firmware of the mixer from v1.3 to v2.0. But only catch is you have to do this update via your old PC or laptop that has XP/Vista or Win7 because Win8 won't allow you to update the mixer's firmware. Also you have to follow the instructions in the "read me" file that comes with the firmware. So basically the problem has to do with the firmware of the mixer that has to be updated. And now I can record and playback all my multitrack recordings.
Thanks once again everyone for your help.