I replaced the door speakers in my XJS today with 6 1/2 in speakers. ( actuually the dia. is 6 in. with tabs that stick out 1/4 in from the dia. So a 6 1/2 in. speaker.) I first installed 5 1/4 in speakers and they were terrible. I did not know what the wattage of the radio was and I had 45 watt speakers. They were horrible. I think the radio is 80 watts. Took them out and went to Best buy and got Kicker 100 watt /300 watt speakers. I haven't tackled the rear ones yet. I think they will be a %^$@*! to install. The hardest part is removing the trim and Drilling new holes to mount the new ones. The old speakers literally fell apart and they had a 6in diameter with 3 hole mounting. There is no such thing as a 6 in speaker that you can use.

 

I don’t think I was able to fit Kicker speakers in the front. Too deep, or the backside of the speaker would not fit in the hole. I forget. I put in JBLs. Very happy.

The rears have basically no limit.

Not all 6-1/2” will fit up front, without modifications anyway. I’m pretty sure I posted my experience on this forum a few years back.

 

I've replaced front and rear and don't remember the rears being any more difficult

 

How easy / difficult is it to get to the rear speakers? Think I saw in the Service Ops Guide that it required rear seat pad removal etc, but then I saw an write up online where I think he basically prised away the panel with the speaker grille, after just removing the 'shelf' just in front. My '91 4.0 will definitely need new speakers one day, the origianl ones are well past their prime.

 

The stock speaker size is 4" fyi. No mods needed

 

The OP has a 96. That model year has 5-1/4" speakers all around.

I was able to fit 6-1/2" JBLs and Alpines in there without any modifications, but only specific 6-1/2" speakers will fit without modifications.