In Mainstage 3, how do I auto sample a hardware synth using a Steinberg UR22 MkII audio interface. My Laptop is a MacBook Pro.

The instructions tell me to select the "type" as "External Instrument" to an added channel strip. When I add the channel strip there is no selection for "type" but it gives me the choices of "Software Instrument" or "Audio" or "Aux" or "External MIDI". Which one should I choose? When I tried it, I chose "Audio". I plugged the audio output of my synth into "Mic/Line" input # 1 on the UR22. I kept the MIDI Out from the synth to go to the USB of the laptop, which is how I always wire my system to play my synthes through the Mainstage 3 system. It's a MIDI In & MIDI Out to a single USB cable that I use, like a "Y" chord. I then also plugged the other MIDI end into the MIDI In on the synth. I chose the auto sampler and when I pushed the keys on my keyboard, no sound came out of my amp. But when I pushed the digital key on the screen within the auto sampler, the sound of the synth came out of my amp. I started the auto sampler to sample the instrument and I could hear it going through my amp. I saved the sample and then brought it into the channel strip via the EXS 24, but when I play the actual hardware keyboard no sound goes through my amp. What am I doing wrong?? Any help would be appreciated. Thanks Boeapple.