I was able to buy the 400 ES at a good price on Black Friday. I use the Fast-Linear PCM filter without Sound Color and the sound of classical solo piano recordings, which is very important to me, is really convincing. I'm currently listening to a lot of recordings from Glenn Gould's Remastered Collection, which I digitized myself in FLAC format. The piano sound is present and free of coloration and the master's singing in the background is always present. Whether this DAC sounds so much better than my old one, who knows, but I am very satisfied with this device and the exterior also looks very high quality.
For me, solo piano music is a good source for evaluating consumer electronics. I remember with horror the sound of the first CD player with the Technics MASH D/A converter many years ago.