Maybe Leaving SET for Solid State because I want bass

OP, I know you decided on Atmasphere’s Class D amps, but out of pure curiosity:

• Agree with adding subwoofers, but presuming this was never in the cards for you for natural reasons such as aesthetics or space constraints which is understandable. 
• When you used tone controls you stated “the tone controls showed just how much bass the speakers were capable of, even if the rest of the sound was less than ideal. Why no one makes a modern high end preamp that has tone controls is beyond me.” Did you feel that your amp had a good grip on the woofers? Or did you feel like the bass was a little loose given the innate limitation of your SET amp?
• If satisfied with the bass presentation utilizing tone controls in conjunction with your amp, Decware makes a very transparent tube-based equalizer that does wonders, which can be found here. I know this is after the fact + the long waitlist, but it’s an alternative to the Schitt  equalizer that others have mentioned.

I absolutely love the aesthetics of those Diatone’s. Curious about your experience with Atmasphere’s Class D amps - please report back. I’ve been looking at both Atma-Sphere and Laiv’s GaNM amps for the summer down here in Phoenix.

IMO, anyone doing measurements that doesn’t have a way of dealing with that isn’t playing with a full deck. Get a variac for heaven’s sake! Then you can insure the line Voltage is correct by doing measurements. 

Not sure why this came up but if you are worried/wondering if your line is sagging, and not producing full current consider a simple plug in meter like this one.  If you find it is sagging, I think maybe Ralph ( @atmasphere ) meant to suggest a voltage regulator, which can be had via PS Audio regenerators or much more affordably from Furman with a conditioner that has has actual voltage regulation. 

@erik_squires This comment was made in the context of making measurements of an amplifier's output power. If the amp is high power, IME the line will sag as you run the amp up to full power so a variac is used to correct the line Voltage at the input to the amplifier to the Voltage for which the amp is rated. 

If this is not done the measured full power of a higher power amp will not be accurate. 

We have used a variac at audio shows, where line Voltage is often quite a bit less than it should be, in order to have our equipment running at the right Voltage. 

Parasound Halo JC 5.

or

Add a sub using speakon connection.

Mitch2 may be correct, why mess up what you already have accomplished, just add a good sub like Rel. After all quality sound is important for musical enjoyment as well. My problem is the opposite; I have too much bass and right now have no room to move the main speakers around. It sounds sensational but the bass although tight and tuneful is a bit too much on longer listening levels and I doubt if the neighbors like it either.