Hi,
That seriously drifted... sorry about the delay. I finally got my head around working this out. I faced lots of trouble on this, but it's available now.
So, not only you can now select a different Collection ( point to the Collection prefab itself), using the sprite name as a string will now work. it was buggy.
I have informed te author, so it's likely going to be features in the next release in the goodies package for PlayMaker.
[EDIT] it's now on the official 2d toolkit package.
Bye,
Jean