Preamp for a GaN-FET amp...

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.

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 future for audio amplification is GaN FET and other flavors of successor generation "digital" topologies. Class A and tube amplification generally will become even more of a niche product area as the generation that brought those technologies back, mainly to high fidelity, leaves the market, which one way or another will happen. Tubes may sound lovely, but enough people need to be buying them to make their manufacture worthwhile. The Chinese domestic tube HiFi market will probably become the mainstay for market demand, as long as their government permits inefficient electrical goods to be sold under whatever decarbonization policies have effect there. If the Chinese leave the tube production industry, tubes are done. No worry, some clever engineers will find a way to recreate the tube effects in a digital topology for those who can't do without. 

To the OP: Peachtree has a couple of GaN amps, at least three now, two of which are standalone amps and the third an integrated. You didn't say what your requirements were or a budget, but the integrated they sell is $3K and has 200W power.

You might look at the Pro-Ject Pre Box RS2 Digital preamp. It offers dual DAC, a headphone amp and a selectable tube output stage. It has an I2S interconnect for use with the ProJect CD transport, but will work fine with any streamer or CD player.