@Andy KU7T - Since the product (PowerGeniusXL) hasn't launched nor have final documents been isued, you can ask Ranko 4o3a first hand via the forum and/or support on his main website Http://www.4o3a.com for exact details on his amp.
But your real issue is the base K2 lacks a PA-Keying output. I think the KPA-100 module for K2/100 may have added one, otherwise you need to put in mod like Tom N0SS's (was linked form Elecraft's webpages). http://www.elecraft.com/Apps/Amp_keying_ckt.htm
The "Key" on the K2 is for your code key input.