Preamp for a GaN-FET amp...

Is fear of tubes a mental health issue? Tubeophobia? Saying you don't want a tube preamp but you want something that sounds like tubes seems like a paradox. Tubes get too hot? You like to shoot BB guns at your hifi rig? You need to change them out from time to time which adds a depressing new stress on modern life? A bout of cherophobia? (look it up) Most all high end preamps are Class A by the way, so that criteria may dissolve. Regarding tube replacement stress, my good ol' original version Schiit Freya has had the same quartet of NOS GE 6SN7GTB tubes for a couple of years...no sign of lost fidelity, microphonics, or anything else to make me want to replace them. 

The Topping pre90 is PIA to try because it has too much gain. It works with amps like the Parasound A21+ and Benchmark AHB2 which have adjustable GAIN. I ended up getting rid of it after it did not match with a lot of amps including the LSA Voyager 350 GAN.

The 2 preamps I recommend with all the GAN amps I have had and also all amps are the Holo Serene and Benchmark LA4. I also like the new Schitt Mjolnir (sp?). It is a headphone amp but also works perfectly in 2-channel. I have it setup as 2-channel but for for headphones. It has a Class A sound to it, unlike cleaner sounding Serene and LA4.

I did love what the Mjolnir does with the Class A Schitt Aegir amp into my phones. As a frame of reference, I feel the Mjolnir is way better than the Schitt Freya+ (I sold the Freya+).

The best GAN amp I have had and likely better than any GAN amp is the PeachTree GAN1. This piece is definitely leagues better than any GAN amp I have had, the PeachTree GAN400 and LSA Voyager 350 GAN, Now the stock version is not anything to shout about but get a $500 modded version from TweakAudio.com and you are in business.

No preamp, no DAC, no interconnects, no amp needed. It is all in the GAN1 but it only takes a SPDIF stream as input and has no volume control. Of course, this will work perfectly if you use the correct tools. The simplicity of this unit is what makes it something special, again I AM NOT TALKING STOCK.

I have a number of customers with one of these, I have only heard positive things:

Topping Pre90
Gustard X26
SMSL HO200

The amps have an input impedance of 44k, making them easy to drive with pretty much any pre-amp.
 

What’s your budget for the preamp Z.

the most versatile is the Linear Tube Audio , if balanced using top Lundahl transformer retail$5800 but has 3-4 vacuum tube choices , and several gain settings.

I found moving from the Belles Aria to the Aria Signature made a significant difference, since you do like the Belles...

Have you considered updated crossovers for the 620's?

DeKay

I kind of went down the same path.  Moved from tubes to class D (AGD).  I had a Cary SLP-05 and found the combo to be wonderful in my room.  I tried running DAC (Bricasti M3 at the time) directly into amps and found missing a little life and soul.  Cary turned out to be the ticket for me.  

@alaindexe I get trying to move away from tubes. But I think you'll find that the common wisdom is still to use a tube preamp with the solid state (in this case, GaNFET class D) amp. Our class D is designed to be easy to drive with any kind of preamp.

Well. You are really just proposing a sideways trade. I have never had good luck with these. Typically you are trading one set of strengths and weaknesses for another. So, whenever I have done this, I have been really disappointed because I lost some qualities I really liked while maybe gaining one thing. Also, you’re fishing at the very bottom of the barrel. 
 

My approach would be to enjoy what you have until you can put 2x the investment in the preamp/amp. Typically if you are very careful and research well, you can get what you wanted, without the disappointment of loosing something you had.

What’s your budget, and are you looking for new or used?  BTW, many SS preamps run in Class A but only get mildly warm due to the low-level signal so maybe not much of a concern.