What preamp with your GaN power amp?

I am feeding my Voyager GAN amp with the Don Sachs tube preamp.  It is a blissful sounding combination.

Well not a GaN Class D but I use Audio Research sp16 tube preamp with Bel Canto ref1000m Class D mono blocks and that is a match made in heaven.
Which GaN specifically? The input impedance is the key spec for any amp type to know that will help determine the right pre-amp. Nothing special in this regard with GaN designs. The input stage design is what matters always. Tube preamps have high output impedance. With a tube preamp in general I would go no lower than 40-60 kohm input impedance on a matching amp to be sure things perform well with good dynamics and lowest distortion for detail, imaging and soundstage. For example Ref1000ms are 100 kohm input impedance designed to work with most any preamp. That is a big reason why I ended up choosing it.   I would do same for a GaN amp with tube preamp. Good luck!

When John Darko recently reviewed the Peachtree GaN, he used the matching Peachtree DAC/Pre with good results.