They are probaby only getting like 7 watts as it is. Anything much more and they will be destroyed. Cheap coaxials can be had for like 40 dollars on eBay and online stores. You'd be happier with better speakers.
Hey Richard, my wife has a Cadillac also. I gotta do pretty much the same thing. Here is what I need to tell you: the 6 x 9's are 10 ohm. Just a little something the good ole boys at GM did to protect their precious wimpy speakers. I am pretty sure that a 10 ohm impedance has to have an amp because that Delco HU ain't gonna push enough power at 10 ohms to drag a greased hair out of a gnat's butt.