Sure, I use the Soloist 3x as a headphone amp and as a pre-amp to active monitors/speakers.
There are too many buttons that need to be pushed or held. The switch would have been preferred.
For example, to enter into power amp mode - low gain. I need to press the menu button, turn the knob to headphone out, then turn the knob to low gain, then hold the menu button for over 10 seconds.
When I want to use the active speakers, I have to hold the menu button for over 10 seconds to exit the power amp mode. Then click the menu, and turn the knob to medium gain. (Low gain isn't loud enough for active monitors).
With I.E.Ms, on medium gain, there is an audible hiss (loud hiss on high gain). On low gain, it's dead silent.
With headphones, the drivers do not pick up the hiss like I.E.Ms.
I noticed an increase in sound separation on low gain power amp mode.
In non power amp mode, I listen to ~45-52 on medium gain, with a 5v output DAC (Gustard x26pro).