First off, I don't jam while flying so I have no idea how to hook this up, but I'll give it a go.
First, don't spend the money on Sporty's gizmo. If you want to listen to tunes in the cockpit, here's what you will need. I'm pretty sure the ERJ has a jumpseat audio panel as do the CRJ's. Go to
http://www.flightcom.net/site/products/accessories.php and order the 3.5mm on one end and the mike jack on the other (part #
103-0613-00) Radio Shack does not sell the MIC jacks since they are aviation specific. They do sell the Headset jack, but this will not help you.
Plug the 3.5mm into your MP3 player or portable DVD player or whatever, and plug the MIC jack into to MIC slot on the jumpseaters panel. Use the jumpseaters Comm panel to adjust volume either by the device itself, or using the Intercomm volume on the jupseaters panel. You will hear it through the speakers if you have them turned on as well as your headset if it's plugged in. However it will not shut off when you transmit, which is no big deal since it won't transmit from your PTT switch.
The cord is not stereo but works fine since most of the speakers are crap and not stereo. If you want to play it in the cabin, you will have to select PA, and hold down the MIC switch to hear it.
Again, I have never done this before and have no idea what I am talking about.