Why? (Does the signal degrade in this circumstance...)

This is for my edification and not a post In Search Of the absolute sound:

So I've got a Schiit Gungnir Multibit that I'm enjoying quite a bit.  It has 2 single ended outputs and one balanced output.  Using the balanced output and one single ended output does not appear to affect the quality of the signal on either output. (The balanced to a BAT VK-3i and the SE to an Emotiva XSP-1)

However, plug in the second single ended output to my Levinson ML-26 and listening to that preamp, the signal has additional gain when the Emotiva is turned on and the Schiit selected on the input.  Turn off the Emotiva or switch to a different input, and there is reduced gain on the DAC through the ML-26.

WHY?  Is it that the input impedance on the Emotiva goes down when it's turned off or switched to another input?