Its tough to make a fair comparison - bare bow to bare bow.

I have found Vibration to be due to a few things.

A bow backed off in poundage tends to vibrate more.

Whats on the string is real important. take the Mathews rubber string stops off and install Bowtechs hush kits on it - would be a more fair comparison.

I still think leaches work better than the stock kit on Bowtech.

Add enough weight to the Liberty so it weighs the same as the Outback would also be a better comparison.

A bow with a longer DL will vibrate more than one of the same with shorter DL.

I have found both bows to be very "vibration free"