Center Channel Dialogue

My experience, with a lot of measurements, is that where you put the center matters a lot. If you stuff it in a shelf it’s going to be very bassy, but there's a lot of other things to look into.  Lets start with basics.

1.  Speaker

Make sure it's operating correctly.  Turn off any auto-EQ/room correction and listen to it up close.  Does it sound good with your head 1' away?  You can also try hooking it up temporarily as a main speaker, as a diagnostic.

2.  Room and placement

With an ESL center you also have the issue of that rear reflection. My suggestion is to focus on eliminating rear reflections first, try to raise it as close to the bottom of your TV, and then take a surgical scalpel to excess bass resonances.

Use a comforter/blanket behind the speaker to experiment and see if that’s your problem.

Same problem with old Infinity Video one, wife had trouble with dialog. Just upgrade to a Kilpsh KCF C-5. Wife loves it. I am not a big fan of horns but in this case the horn tweeter works great for vocals. And the C-5 must be pretty damn efficient as I had to turn down the dialog lift on my Yamaha AVR.

Good suggestions, and I can clarify a bit...

I have experimented quite a bit with levels of the front and surround speakers, and the level output of the center is much more. 

I have also compared large and small settings for the center, but it did not improve.

Very important is the mention of age/hearing. I'm almost 68 and am sure high frequencies left town years ago. However, some movies I watch have little issue with dialogue making my hearing less a factor. It's more that quieter dialogue is hard to comprehend unless I cup my hands over my ears. 

Yes, it is my concern about mixing technologies (electrostat vs dynamic) would sound wonky, but when I listen to music, I listen in stereo only, unless it's a SACD with surround capabilities. 

The electrostatic panel sits 28" from the front wall. I have a 85' TV panel wall mounted. I have also tried a piece of sound proofing board behind the panel, but it sounds better without.

So far, the only thing that helps is cupping my hands over my ears, which is why I thought of a horn based center.

@erik_squires made some really good suggestions to try.  If they don’t work I’d recommend doing a trial of this SVS center speaker.  They offer a very generous 45-day trial period including shipping both ways so no risk whatsoever to see if it works for you in the context of your excellent system.  If dialogue isn’t clearer through this you’ll at least know your problem lies elsewhere, but my guess is this will fix your issue and at only $800 won’t break the bank either.  If you do this I’d suggest listening with the grill off, and let it break in at least 100 hours before making any firm assessments.  Hope this helps, and best of luck. 
https://www.svsound.com/products/ultra-center

I am now 76 YOA, and I have no trouble hearing my center channel. For years, I used a rather small KEF center, and it worked quite well. A couple of years ago, I did a bit of upgrading on the HT part of my audio system. I bought a new KEF Q 650c center, along with some nice Pioneer surround speakers designed by Andrrew Jones, (which sound wonderful).

Center channel sounds clear, clean, and smooth, very easy to make out dialog.

Good luck in your search. Regards,

Dan