Benz SLR Gullwing, not sensitive to loading?

You should definitely hear a difference from 100 ohms to 47k. Sounds like something's off in the loading setup, though I can't guess what that might be. The signal loss from 100 ohms loading, on the 38 ohm SLR or LPS coils, is almost 3 dB (versus 47k) - which alone should be extremely audible, and will surely come with frequency response aberrations on top of that.

Signal Loss at 100 ohms:

20 * log(100 ohms / (100 ohms + 38 ohms)) = -2.8 dB

Signal Loss at 47k:

20 * log(47000 / (47000 + 38)) = -0.007 dB

Personally, I felt my LPS to be lackluster with 10x SUTs loading it around 470. It did much better, and came alive with an active JFET stage loading at 1000 ohms.

When I use my Benz LPS with an Aesthetix Io Eclipse dual power supply phono stage I use 47k. This setting sounds best to me. I arrived to this setting after a long period of experimentation. I appreciate the mathematical formulas to generalize on average settings, but, after being in this hobby for such a long time, I have learned that there are sometimes no absolutes when it comes to actual connectivity of a slew of components and the intended sound outcomes due to a confluence of factors affecting the sound. My tonearm is an SME V with analysis plus silver Apex phono cable.

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.

Does anyone else here has a Benz Gullwing (or LPS = same generator) wich does not react to input impendance?
I's on a Clearaudio Ovation with TT5 arm. My phono stage is a Graham Slee Reflex C in wich I just soldered 47kOhms resistors when I got the cart, before was 1kOhms.

Now I ripped some tracks to my computer to see if 100, 1k, 22k or 47k sounds better using a Y-connector with resistor. And there is not the tiniest difference in sound at all. Plus the three tracks even have the same volume level. I'm not used to that because all the MC cartridges I heard before sounded (more or less) brighter and the level dropped a little bit when I raised the loading.

Is there something wrong here?

@tealow Not at all! In fact this is good. The reason to use a loading resistor isn't for the sake of the cartridge, which does not 'ring' at audio frequencies, its for the phono section.

This is because the inductance of the cartridge is very low and also has a high 'Q' value, and its in parallel with the capacitance of the tonearm cable. Together they form a very peaky resonance at a very high Radio Frequency (RF, possibly above 1MHz) and when this peak is energized, it creates RFI (Radio Frequency Interference) that is injected directly into the phono section.

If the phono section doesn't like that, it won't sound right and so loading resistors are used to detune (make less peaky) the resonance, thus removing the RFI.

If the phono section does not care about RFI then you won't hear a difference until you get the loading so low that the output of the cartridge actually goes down.

In short, you're in a good spot so no worries!

47K is the industry standard loading and if the phono section is properly designed this will work fine with all low output moving coil cartridges. If you have to apply loading to get the 'right sound' the phono section has a design issue.

In practice, I find what Atma-sphere says to be true as regards loading LOMCs at 47K ohms, although sometimes I slightly prefer lower values of load R just "because" I can imagine I hear a tiny difference. On the other hand, if you don't hear a problem with a 100R load on a Benz LPS or the like, then something is amiss (because there is a mismatch between a cartridge with an internal R of ~30 ohms and a phono load of 100 ohms, such that a large fraction of output V is lost to ground AND you have a high frequency roll-off within the audio frequency range), as Intact says.  You got great advice from two industry professionals.