StarTekh
http://www.fender.com/en-...are-firmware-downloads Fender Universal ASIO Driver 2.10.F (Windows 7)
+1
I'm not familiar with the Mustang Floor, but I have the Mustang II amp so I guess they'll be similar. You need to install the ASIO driver from the above link then SONAR will see it in the list of audio interfaces in Preferences/Audio/Devices.
Note the USB interface is input-only - you'll need to monitor through a different interface.
If you haven't already done so, download the latest version of Fender Fuse from
here - this will let you deep-edit settings, store and recall presets, etc. also will allow you to download the latest firmware.
I'm very impressed with my Mustang amp - I hope you have a great time with the Floor!