Cannot comment on the Syncpack from experience , but adding that weight on a normal pack takes you over the weight of the Aarns.
Some have added the Aarn pockets to an existing pack but the system works much better than split.
The Aarn advantage is the gap in the middle, the fact that the pockets don't rest on your chest and the larger volume .
They share the counterbalance effect and ,possibly, the weight transfer to the hips.
A bit fiddly at the start but feels great once you get it right.
Franco
BTW, loads of video clips, hiots and tips on the site :
http://aarnpacks.com/