i have a mazda rx7 and bought a protege head unit. im not sure if it is six disc or not and was wondering if there is a way to tell before having it installed (thinking about an aftermarket head unit instead but if this one is 6disc I will just put the the oem one in)

This is the actual head unit.

 

Hmm, I'm trying to remember if mine actually said 6-disc changer on it or not. Well one way to find out is to take and power it up. Use jumper wires to power the h/u and see what shows up.

 

that is NOT a 6-disk....on the left where you see the DISC button that would say LOAD.