@pdreher The Topping pre90 ($600) worked with 2 amps I tried it with, the Benchmark AHB2 and Parasound A21+. Both of them have gain adjustments. I tried 5 other amps with the pre90 and the volume was too hot on all of them. When the pre90 works it sounds like the Benchmark LA4 preamp (or HPA4). The LA4 is more robust than the pre90 in that it works with all amps, and it has more features. I kept the LA4 to replace the pre90. I actually sold the Benchmark HPA4 to try the pre90 but I then found out the volume issues and bought the LA4. When the pre90 works it is excellent but bare bones.
I bought the Freya+ to try a tube preamp with my gear. I knew I could sell it easily. The Freya+ compares more to my tubey CODA 07x preamp. The Freya+ is actually quieter than the SS 07x. However, the CODA 07x is more detailed, not as warm but does add warmth to the sound (unlike the LA4). I find the 07x a much better preamp over the Freya+, but it also costs about 7x more.
When I have my best combos, I prefer my LA4 over the 07x by a bit. I love the neutrality and pure silence of the LA4. However, there are gear combos I have where the LA4 does not work, the 07x always works with every combo.
The Freya+ also worked with all my combos and is a very good preamp. Great features and very good sound (I used the stock tubes). It was a revelation with my bright RAAL SR1a headphones | AHB2 | Muertec 005 DAC. Much better than the LA4 and a bit better than the 07x.