DK design vs1 MK ll as a preamp?

So I decided to take out my old DK design MK ll integrated amp and rotate it back into my system. I never bothered with this before but I have a tube amplifier that I wanted to connected to the DK and use the DK as a preamp. The DK has line outputs. I was told years ago when I first purchase it that its not a variable output? Has anyone tried connecting an amplifier using this line output? I'd love to hear from people that indeed tried this with this DK