Wow, it's scary that you have people working at a music store with such incompetence. It reminds me of a story my old guitarist told me. He needed a new jack for his EMG-loaded Charvel. He went to a local small chain (not a GC) and asked for a stereo jack. The GM was rather incredulous at the request: "Guitars use a mono jack!" My guitarist explained that, normally yes, but active pickups require a stereo jack. The GM got more belligerent about it. Finally, the GM called someone at the sister store, and then stammered about after getting off the phone, "Uh...yeah...technically you do need a stereo jack...but you can use a mono jack as long as you take the battery out after you're done playing."
My guitarist went to RadioShack and picked up a stereo jack for his Charvel.