volume

I've got an ex-dem Leema Libra DAC connected to a Hydra II Anniversary Edition power amp [on loan]. The DAC turns the volume down by itself within ten minutes of switching on. However, the displayed volume level does not change. Does anyone know what is going wrong? It's connected to the amp via...

While running some tests with my Rega DAC (1. gen) and a Topping D10s, I noticed that while running the source directly to the Rega DAC's USB input the volume was fixed (which I prefer), but when running through the D10s to get Coaxial SPDIF out in 24/192, which the Rega does not support via...