In the jet pack is the only way to go!

I've have both of my Jango Arena Jet packs set up this way, run the wire out the back of the jump suit through the vest and just under the arc in the back plate and plug in right into the a jack mounted in back portion of the pack that's hooked to a RadioShack amp, it's pretty slick I think! 8) It also actually helps amplify the sound too!
I've included some pics for some quick ref.
P.S. As a side bar for anyone looking, this one's up for sale.
[ATTACH=full]11682[/ATTACH]
[ATTACH=full]11683[/ATTACH]