Replaygain is already set to disabled. I can try renaming the file to see what that does. I might work round it by providing a silent track to be the first item on every playlist followed by the real track I want. Then I could set it playing before switching the amp on. The pop might be a DC level or burst of noise when play starts, or it could be the sound card being woken up.
The bad first run is a different matter. It's tedious to have to go through the rigmarole of start, delete socket and start again every time I want to play music.
Apart from that, it actually sounds very clear with precise stereo imaging - better than when I ran it on Puppy, though I can't really understand why. After all, surely the tracks and hardware are what determine that, not the player.