Easy to drive, outstandingly natural sound from 40-50 Hz up.....AN-E, O/96, others?

Hornings would check all your boxes. I see that not to many Horning owners on Audiogon. That’s too bad because they flat out play music!
You can use SET amps with no problems.

Mitch some great options listed here, I have AN-Js myself, but just wondering since you keep mentioning a 50 watt amp do you have a particular amp in mind? I took a look at your system, it's pretty awesome looking, as SS amps go I bet those Claytons are pretty sweet. You mention liking the setup so is the move downsizing or just curious to try something new?

I one owned a pair of speakers that sounded hauntingly beautiful with a low powered SS amp: the original JM Reynaud Ofrande speakers, made in France.  Absolutely beautiful looking and sounding speakers.

I ran these with an Atoll 80w SS integrated amp and it was a perfect match.  These just didn't work in my room (long wall, fireplace, couldn't pull them out enough into the room) but I can honestly say that these are the ones that got away.

There's a pair of Usher BE-10 DMD's on AG right now I think would fit the bill. they're big and heavy and have a look you're either going to love or hate, but they offer all the resolution we expect from a modern hi-end speaker and manage to throw a wide deep sound stage. musical and engaging, and sound really good right out of the box without hiring a crew to set up and tune your room for.

I like AN-E's that you mentioned and recommendations for the Spendor SP100.  I don't know what price range you are looking at, so as a broad mention of speakers that will probably work well with 50 watts, the following brands are worth looking into: 
1. Tekton (I heard their $3,000 model at a show and it sounded quite good.
2. Charney Audio--I've heard a $13,000 and a $17,000 model (same speaker with different full range driver) and both were VERY good, particularly the $17,000 model with the AER 3 driver).  
3. Rethm Bhaava--this is a $3,000 speaker with a wide range driver and a built-in powered subwoofer that sounds great for the price.
4. ProAc--I like a number of models in their lineup.  Although not that high in efficiency, their speakers sound quite good with modest power--must be easy to drive.  I particularly like the big D48R floorstander and the D2 stand-mounted speaker.
5. DeVore Gibbon X--perhaps not as low-power friendly as the O 96 Orangutans, but I heard them with a 30-watt Luxman integrated and the combination sounded quite good.

Good luck in your search.