Kinki Studio EX-M!+ owner here. I think the amp is great. I primarily use it with Buchardt S400 MKII speakers which are 4 ohms and the amps has no trouble driving them with authority. I also use them with my Triangle Comete EZ with great results.
On the volume front I'm usually between 60-75 when listening to vinyl which will have the music in the 75-85 DB range. When listening to digital I'm at 55-65 on the volume dial for 75-85 DB range.
I can push the amp and speakers to uncomfortable listening levels without distortion.