Thanks to FRCTX99, I got my covers off and managed to install better 6.5 inch speakers in my Coupe's rear today. The secret was to pull harder than I thought was reasonable to get those dam covers off! Then the next hurdle is the fourth screw that some GM nimrod decided to put at the top, above the inside panel. I had to pop the panel loose and even then it was very difficult to remove that fourth screw! Anyway, got it out and decided to forget about putting the new one in that position - it only needs three to hold it anyway.
Here's a little of my analysis that led to my purchase decision. BTW, I have a 2500 dollar audio system in my Maxima with Boston Accoustic speakers and sub, three amps, and a good Sony head unit. But, obviously, the Blose system in our C5's falls short, right? The biggest problem is those rear speakers. The front units are really OK, and sound pretty good, but the rears don't add any value to the system. I decided to go cheap on the rears; I wanted an improved sound, but knew the fronts would be doing most of the work. I listened to the selection at Walmart and found a Pioneer, Mdl TS-A1664 for 70 bucks that fit the bill. These are a direct bolt-in replacement for the truly horrific Blose units the General saw fit to put in a 50K sports car :U And, they sound pretty good.
Now, with the fade control at about 10-11 AM, I have some depth to the sound and what's coming from the back is decent. The whole system is transformed. Pink Floyd's The Wall was 85 per cent of what it should sound like. Still no truly deep bass, of course, but whaddya want? There's no sub in the system, and I probably won't add one.
Anyway, thought others might like to know about a really good use of 70 bucks if they don't want to go further with the stock Blose unit.
:cheers: :seeya :cheers:

 

I had the exact same problem with the top bolt...my solution was the same as well..only use 3 on the new speakers. I used some infinity 652i with the tweeter that you can move. I also found that putting the fader at 10:30 sounded best.

 

This is an old thread, but I thought I’d share a tip that worked for me. I swapped in a set of speakers I found in my garage, and agree with the 10:30 position on the fader.

After trial & error on the first side, I finally found a method that allowed me to install a speaker on the other side in 20 minutes start to finish with all 4 screws!

Use a flathead screwdriver to "lift" the panel so you can access that top screw with a wrench for removal. Then, for install, I have slotted holes on my aftermarket speaker, so hand starting the screw (again, using a flathead to create extra space) allowed me to slip the speaker in then tighten after.

I wouldn't say this was a significant upgrade, but I'm happy with the result since it was only a little work (did this on my lunch break) and zero dollars out of pocket.

 

So the speaker grill just pulls out? I was thinking the whole 1/4 panel trim piece needed to be removed.
Did you just pry it out?

 

This may already be known but yes, the rear mesh covers can be removed without the whole plastic panel. Gently pry on upper corners and middle, they should pop out. If you want to remove plastic body panels, I highly recommend getting a panel puller tool set - I got one on Amazon for pretty cheap and it helps greatly compared to a flathead screwdriver (which can damage things).