I’ve used the spl monitor controllers for 4 or 5 years…both the stereo and the surround versions. They are fairly good, but at low levels on the attenuator (which is stepped) the levels in each speaker do NOT match well. Also, at high attenuation levels, the audio quality suffers. Once you reach the third or fourth step, things begin to behave much better… I actually tested this with spl meter and spectrafoo… I thought I might just be making things up, but it turns out (at least on the 2 units I tested) there were very measurable differences at these very high attenuation points. I got around it by using attenuation on the speakers, so I’d rarely go to these very low levels on the m/controller. Then, about 18 months ago, I set up the control room in Nuendo properly, and got it to play very nicely with my metric halo I/O. Have not looked back. Use a knob on my euphonic to control the volume, which, although the knob is poor quality, is very very usable. I’ve replaced the small diameter knob with a larger one, which makes it much easier to use accurately.