The plan is to try various combinations and see what sounds good. The front speakers are new Infinity Kappas and already sound pretty good. The old rear midranges are still in the B pillars. The new rear speakers are 6.5" bass mid, going into the lockers, so I can run them as full range rears, or subwoofers. The locker lids will have a bass reflex port tuned to 60hz, just below the Fs of the 6.5" speakers.

The new amp is 4 channel bridgeable into two : 150wpc in bridged mode.

I'm going to try the new rears as full range, and then as subwoofers, both via the new amp, bridged. If the bass still doesn't cut it, it is a pretty simple matter to make the holes in the new locker lids bigger, and put 10" subs in. I measured the lids, you could get 10" drivers in if they aren't too deep.

But I wonder about the relative merits of putting in a good pair of full range 6x9s, driven by the amp.

 

In the rear, IMO completely useless because you will get frequency cancellation and frequency addition at certain frequencies affecting the frequency response, depending on the distance between the speakers and your ears this can cause either - boomy, tinny or shouty effects. In other words the music will not sound smooth.

Since you have quality Infinity Kappas If it was me I would not add more speakers, just a woofer to complement the bass. Since the Kappas are 95dB these will only need a few watts.

I have 4 speakers 2 fullrange in the doors and the 2 woofers in the rear crossed over at about 100Hz.

 

I got around to doing the wiring tonight. What I did was use the output from the 35A fuse for the heated rear window. I have an XJSC, don't have a hardtop, just the softtop with no heater. So the chances of ever needing it are nil.

I unplugged the relay (behind the headlight switch), and plugged a spade terminal into the plug. Simple.

 

Great solution. Congratulations
Greg

 

That's how I ended up, rears as subwoofers crossed over at about 100hz. System sounds great. Instead of giving the front speakers full bass boost, as I did previously, I can now have the front speakers set flat, so they play louder with less distortion.

The little Kenwood amp has enough power to bottom out the rear speakers, so I guess that means I have enough power!

 

If you use the rear outputs on the head unit to drive the rear woofers through a 100Hz low pass filter you can use the fader to adjust the response at the X over

 

This unit can switch the rear outputs to subwoofer mode, which then gives control over lots of stuff.