I was cleaning the ground that is by the battery and there are 3 star shaped metal washers between the ground wire and the frame can i remove these to help increase the area of contact or can i just remove one of the bolts on the side frame that will be easer to sand for the ground. Also where would I hook a voltemeter to check the differences in the performance

No. The area of contact will remain largely the same anyway, plus the star washers are used to provide some "bite" between the metal surfaces, so that you don't just have one flat metal surface clamped against another. If you did, water would infiltrate between the two flat surfaces by capillary action and eventually kill the conductivity. So take it apart, wire-brush where necessary, wipe a thin film of Vaseline petroleum jelly or dielectric grease on the parts, then reinsert the star washer(*) (not sure why you have three stacked up, to be honest; I need to check whether that'* factory) and button it all up again.

You can measure battery voltage across the battery terminals. You can measure system voltage between any orange wire (e.g. your lighter socket) and ground. Can you tell us what problem you're attempting to solve here?

I was just wanting to clean up the voltage some because the back speakers cut the bass out when turned up so far from the treb comming up I have the stock system because my old deck was stollen and with that one being a higher wattage I could turn it up all the way up with out having the problem. I alredy cleaned the ground and sanded it and it helped alittle.

I guess I will just need to go with my original plan of making a crossover to fix this till i get the GP

Okay, well, besides making sure your battery grounds are good, you can always add backup connections on whatever components are supposed to be grounded to the body. i.e. Instead of having several components trying to share a common ground connection, you can add a separate ground wire on each component, going straight to its own body connection. (You can leave the factory ground wires in place, too; in fact you should...)