I'm trying to hookup a Boss RC-300 pedal to Sonar Platinum via USB. I installed the RC-300 USB driver. When I opened Sonar, it recognized the driver. But when I went into Preferences/Audio/Devices, the selections for the RC-300 are greyed out and won't allow me to check them.
 
Here's a link to my Devices configuration:
 
https://drive.google.com/open?id=0B-rVuhGXIf2nWWtpVkhXUVdrWTA
 
Any ideas what I need to do in order to be able to use the RC-300 input/output drivers?
 
Thanks :)

I looked into this a little further. Apparently, I can either use the Fireface drivers or the RC-300 driver, but not both at once. When I uncheck all drivers, it allows me to check the RC-300 driver. What I was wanting to do is record several live instruments using the Fireface and simultaneously record tracks from the RC-300 looper pedal via it's USB connection to the computer. This is similar to when I use an external keyboard via the MIDI USB connection except for I'm trying to stream .wav files. I take it this is impossible?

You cannot use two audio interfaces with ASIO mode.
You need to either use one device or the other,,  
un check all the fireface boxes and select the Boss. Or swicth to WDM or WASAPI exclusive mode. 
I would run a loopback check if you switch driver modes and make sure your offset is syncing up. 
WDM and WASAPI are often a bit out of sync and need the manual offset tweaked. Seems WASAPI is the better of the 2 but still not as good as ASIO. 
There's no damage done flip flopping between driver modes other than Sonar might complain about a missing audio device on re starting when you open the project later under ASIO mode. Driver modes are not saved with projects, they are global. 

Cactus covered most of the ASIO driver limitations.
 
I am not familiar with the Boss unit but what may be preferable is if it has an audio output then send that to your main interface if you want to record from that in realtime which would allow you to continue using ASIO. Your Boss would still be greyed out though in Prefs and you would lose an audio input on your interface to hook it up to (or two if it's stereo output?).
 
For some devices (and I'm guessing this won't apply) that have "Optical/ADAT" in puts/outputs you can daisy chain the units. eg: My old PCI Layla 3g's breakout box has both optical/ADAT in AND out connectors. My Focusrite Scarlett 18i6 has and optical/ADAT input (no output though). With a proper optical cable I can run the optical output from the Layla's breakout box into the optical input on the Focusrite box and have access to the extra analog inputs on the Layla on TOP of the inputs on the Focusriteand remain in ASIO mode (there are some channel limitations/considerations but it does indeed increase my physical input count).
 
Just some (probably not helpful to this situation) rambling.
 
As for the alternate Windows audio drivers Cactus mentioned... yes they are (or at least have in the past) definitely more latency/glitch prone than dedicated ASIO drivers. However Win10 has supposedly improved these audio drivers and intends to continue working on them which will allow us to use multiple devices more reliably. I do not yet own a Win10 system to test this on but the Bakers apparently have and the results were positive.
 
In the (hopefully) very near future I will have a system to test such things on and of course will blather on about the results once I do.
 
Cheers.