Sound unconvincing

I wanted to Teac A-H01 operate on the desk with 2 DALI boxes (Zensor1). Unfortunately, the volume can only roughly set. After only a few degrees of rotation the volume is loud roaring. The sound is very päzise supercooled. Not all of my playback devices have the ability to set a tone control in advance. For example TOSLINK output from the CD player. Since then I can no longer affect the sound. To test, I then times connected large floorstanding speakers and behold, then the volume control works better. I can then use already a quarter of the rotation range. My amplifier is therefore not defective, but not suitable for me.