clocking is needed for digital sync - when you're transferring data digitally, both systems need to be in sync so their samples match up. imagine two people tapping on a desk together...they need to tap at the same rate if you want a clean "hit". Bad analogy but you get the idea.
Positional sync tells you where you are in the song - refers to bars/beats, or time code or whatever.
If you're transferring analogue, you just need positional sync to do what you want to do. If you're transferring digitally, you need both positional AND digital sync.
Unfortunately, none of that helps with what you're doing wrong. If you can post screen grabs of where you're doing the settings, I might be able to help further.