I'm using a Steinberg CI1 interface to record from my guitar into MC6. My guitar is connected to the left channel on the CI1 and in MC6 I always hear the audio in left ear through my headphone irrespective of whether I assign the input source on the track to Left, Right or Stereo of the CI1

How can I position the sound to come in the center? Since this is a mono input, is there a way to set it to mono so the sound does not come from the left? Also, wondering why it sounds the same even when the input source is selected as Right...

you need to select only the left input, not the stereo input for your audio INPUT on your track.

if you select the stereo input it will record both left and right inputs on one channel, but if you're only recording one channel, you need to select only one channel as the input on the track.

Yeah... ditto... you can select either the right of left but not the stereo. 

Choosing the L or R gives you mono straight up the center,,,, and then you can still pan it as you need.

Guitar is, after all, mono anyway.

Use channel one on your Steinberg CI1 and make sure you have the Hi Z engaged for use with your guitar.
You also need to engage the mono button on the Steinberg CI1.
Then when setting up your track in MC 6 pick left as the source.
 You should now have sound coming from both speakers. If not toggle the mono button on the Steinberg CI1 till you do.

Thanks everyone .... I guess I was making a combination of mistakes and messing up my settings ... works fine now ... thanks to all of you for your quick response!