According to impedance bridging principles, are these results accurate?
The general idea is that you get maximum voltage transfer from one stage to the next if the receiving stage doesn't load the source.  Therefore it helps to have the source impedance &lt;&lt; load impedance.  This isn't true for maximum power transfer where you want the source impedance equal to the load impedance, but in audio you're generally looking for voltage amplification in the signal chain. 

Your anomoly is because you are measuring at the output of the signal chain, which may have a varaiable impedance device inside, but there's also lots of other circuitry in the chain.  Without knowing exactly what that circutry is doing and how it affects the signal you can't generalize about the effect of the impedance provided by the VariOhm.