This is clearly indicative to both driver burn in (to loosen the flexible surround),When using stock cables, the loaner is more airy and transparent than my pair. Not by much, but its noticeable.
However, when I run mine in balanced mode, they are the winner: they are more dynamic, there is more air and clarity in sound
And the amplifier damping factor.
Your amp prob have a weak output.
A stiffer cone surround will exhibit more resistance and your amp single ended out is prob weaker enough to hear the difference , while the balanced out clearly pushes the newer unit better.
There is probably a bad batch issue with some units,Has anyone gotten a pair of D7200s with yokes that have a scratchy feeling when the cups are rotated
Because any creaking is a sign of missing internal plastic washers.