Your diagnosis is correct: only the CAD profile is supported, but not CAD+SPD.
We're currently working on the CAD+SPD profile for Bluetooth Low Energy, which will soon be ready. I cannot promise you that we'll provide support for CAD+SPD for ANT+.
I am having troubles to connect Run.GPS with the Garmin GSC10 combined CAD and Speed sensor. Most probably due to not supported CAD+Speed profile by Run.GPS. Sensor works fine with my Samsung Galaxy S4 and different apps. Are there plans to include new ANT+ profiles in close future?
Any hints welcome. Thanks