Benz SLR Gullwing, not sensitive to loading?

As mulveling stated.  the difference in output level alone should be clearly audible.  If the output level does not change as you apply a 100Ω load you are not making a connection somewhere.  A simple way to test this is to simply put a 10Ω load (or shorting plug) into the load position and that should give a clear audible effect of the loading.  Once you have confirmed you are making a connection then you can address the sonic changes.

This is not about whether loading should make a difference. The key statement from the OP is:

And there is not the tiniest difference in sound at all. Plus the three tracks even have the same volume level.

If there is no change in level on a 38Ω cartridge with a 100Ω load, then there is a problem with the test methodology.  Either the applied load is not connected or the level measurements showing no change are incorrect.  Mulveling's first response pointed this out and there is no sense in going on tangents until this obvious problem is addressed.

dave