After listening for a few weeks to the speakers with what I verified was correct wiring, I began changing the crossover to one speaker as mentioned above, and I got it completely built out yesterday.
So others can follow along, here is the corrected schematic. BTW those boxes marked "XFMR" on the schematic should be marked as inductors. When I drew the schematic I was in contact with Jeff and he surmised they might be transformers as they had three connections, not two as you would normally find with an inductor. I think this is one reason he wanted me to send the board back to him, so he could take a look at these strange things. Since then, I was able to confirm with Spendor that they spec or manufacture their own proprietary multi-tap inductors for use in their crossovers. So I am pretty sure that's what they are. :
These are the final changes I made:
Woofer: Those two 20uF electros are now one Solen 43uF film with a 5 ohm Dale resistor in series.
Midrange: The 10uF and 6.8uF caps are now replaced with one 18uF Clarity CSA series; both resistors replaced with Mills MRA 12W; the 4.7uF and 1.5uF are replaced with one Mundorf Supreme 6.8uF.
Tweeter: The 1.5uF is replaced with a Clarity ESA series; the .33uF is replaced with a .5uF Russian MBM PIO cap; the 6.8uF is replaced with a Mundorf Supreme 6.8uF. All caps were burned in on a cooker for 3-4 weeks before I started.
Upon first listening, the sound was completely disjointed and the upgraded speaker was so different than the stock one there was no stereo image at all! I was about to take the board totally back to stock. But then thought it might be the crossover circuit needed the ESR of the electrolytics (I couldn’t understand why Spendor left 2 electros in when everything else on the board is film and the electros are only 20uF, a value that could easily be handled by a film cap.) Still, could this be affecting the entire sound of the speaker? The only other difference from stock values was, at that point, I had pulled that .33uF cap in the tweeter but not replaced it with anything. Couldn’t understand how this would make much difference either.
So fully thinking I would go back to stock, but curious about the ESR issue, I put a 5 ohm Dale wirewound I had on hand in series with the 43uF Solen in the woofer section and also while I was there, put in a .5uF cap in the tweeter section. Also, sensing the 20GA stranded I used for cap leads might be affecting things, so I went to 14GA solid copper.
I hooked it all back up not expecting much, started playing music and immediately knew it was behaving much like the other stock speaker because I had a stereo image and a soundstage again. Checking closer, tonality was essentially the same. I am blown away. How could this be fixed by adding 5 ohms and .5uF? Not disjointed at all now. Same Spendor essence as the other untouched stock speaker, but simply clearer. In comparison the stock speaker has a ‘tizzy’ distortion that overrides everything and it also sounds congested. Always was aware of that congestion (its even pointed to in reviews of the speaker) but I had feared that the congestion was part and parcel to the tonal quality, and if I got rid of that, I got rid of the "Spendor sound". But not true! Could never go back to stock now as it seems so clearly distorted.