Hello Dave, very nice mixer choice. Personally I'm tempted by the smaller webstation but that will take some saving.
Anyway, my guess is that you need to install some sound card drivers.
This should really be a support call to D&R as they are remarkably coy about how the audio of the Airlite / Webstation is presented.
I would hope for an ASIO driver but having had a quick look at the "Aircast" manual it seems that they make the mixer look like a surround sound card to Windows (thus avoiding the need for an ASIO driver).
Sadly, PlayIt Live doesn't support Windows surround sound cards and recent versions will not work with ASIO4ALL (for reasons that I understand but don't necessarily agree with).
The combination of PlayIt Live and the Airlite would be extremely effective but until you get a driver that exposes the sound channels of the Airlite.
If you have another "test" PC, try a version of PlayIt Live prior to 1.12 and ASIO4ALL and you might get somewhere with that.
I would obviously be very interested in how you get on.
I wrote up my experiences with a Windows Surround Sound card at
As a general observation, OSX is much better at multi channel audio than windows, but sadly there isn't an OSX version of PlayIt Live.
If you end up having to buy an external sound card to make it work, look at
for my views on the subject.