In UC Surface, there is a drop down setting for WDM Setup.
This setting is only for the 1394 devices that UC Surface supports (StudioLive Ai and StudioLive RM Mixers).
It is grayed out for Studio 192.
Studio 192 WDM Channels are fixed to the following preset Outputs and Inputs.
Outputs (Playback Tab in Windows Properties):
ADAT Out 1/2
Line Out 1/2
Line Out 3/4
Line Out 5/6
Line Out 7/8
Main Out L/R
Inputs (Record Tab in Windows Properties):
Line In 1/2
Line In 3/4
Line In 5/6
Line in 7/8
ADAT In 1/2
This applies to any applications such as Windows Audio or application that can use WDM Audio instead of ASIO (such as Fruity Loops, Sonar, nTrack Studio, etc)
If you're using ASIO / Core Audio, you have access to more channels than what is allocated to WDM Audio.
See Section 5.3.1 on starting on page 36 in the manual for more information on this subject.