2001 Isuzu Rodeo Speaker Configuration?

I've had my Rodeo for about 3 months now and only thought that I had 4 car speakers, not counting the two small 1" tweeters on the front doors. However I was replacing my cargo light bulb and noticed the two vented holes in the back on either side of it. I took off the panel and saw two, I would say 4", holes with four screw holes for mounting something as well as what looks like speaker connectors. I was just wondering if these were for speakers, every site I tried like sonic electronix and crutchfield say that there's 4 6 1/2' speakers and the 1 inchers. Could neone shed some light on this?2001 Isuzu Rodeo Speaker Configuration?
You could connect up speakers to those and pull out the stereo to remove the bridge so the rear channels play through them.

p411