So I finally spent some cash and ebayed the dual voice coil 4x10 speaker I was talking about. Surprisingly, this thing sounds pretty good. I am running a deck powered 4x50watt Pioneer Premier head unit and this is just what I needed. No dash seperation as expected, but it fills in the mids and highs very nice. For $50 stereo sound, you can't go wrong. Hope this helps someone else in my situation (wanting a hidden somewhat loud, quality sounding stereo). As for the install, the grill just needed some minor filing to sit perfectly. BTW I have 3 way Polk Audio 6x9s in the rear deck.
Jim