Maybe Leaving SET for Solid State because I want bass

I’m with the subwoofer crowd.  I love your setup - vey cool speakers, but as someone else has already said, they will never plumb the depths, nor were they designed to.  I have a very cool pair of restored/modified Altec Lansing Santiagos that are probably rated down into the mid-30s hz region, but when I added a very high quality subwoofer into the mix (MJ Acoustics in the UK), it really made a huge difference.  Don’t give up on your SET magic! You can get a great sub at your budget.

My SET amp sounds lovely and pure but is bass shy

@dhcod Nearly all SETs are. This is a problem caused by the requirements of the output transformer.

There are three ways around it. The first is a kind of SET known as a parafeed. The one I know of in production is made by Bottlehead as a kit. Such amps can make full power at 20Hz, something no regular SET can do.

The second way is the kind of amp Berning patented about 25 years ago. 

Finally you can go push-pull. IMO, if you want the real magic of tubes, you find a lower power PP tube amp of similar rated power to that of the SET. You'll find they have considerably more usable power. 

This is a classic setup for the "never gonna be satisfied for long" audiophile. Going from one extreme - to the other. Why not look at high power push-pull tubes (or at least moderate power), which is where I find the better intersection of "sweet mids" and "bass slam". The bass from tubes is never going to be quite as sharp and clean (with power, body & slam) as SS, but it can hit hard and I’ve found I actually prefer the slight bass bloom / fuzz of really good pp tube amps, versus "clean all day" SS. It’s more natural and enjoyable to me. 

Haven’t heard the Pass SIT amps but I’ve heard SiC-FETs in other implementations (high-end electrostatic headphone amps). They’re said to be "close as you can get to tubes" there too, and let me tell you - WOW they do not sound like tubes AT ALL, to me. Frankly, think I like "regular" transistors better. 

Go nearfield on the main speakers and let them naturally roll off on the bass.  Add a solid state crossover, amp and subwoofer to reinforce the lower range.  

Personally, I don't like the "tube sound" and consider it distortion.  I also don't like "solid state sound" for the same reason.  I have a very clean tube preamp, a tube-hybrid phono stage and honest sounding solid state amps, all Herron electronics  They sound neither tubey or like solid state electronics.  They just sound natural.

Part of this is the fault of a vintage preamp I put in the system for a few weeks. 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. Well Air-Tight does but it's the price of a compact car.