Lamm phono stage LP2.1 Deluxe with low output ZYX MC cart

Any cartridge can be run at any load but is it going to sound good?  No.

What load do you think is best?

Dear @chazark1234 : Your Lamm has no problem to handled that ZYX cartridge.

In the other side and in reference to loading, this issue is something that you are the only one to really say which the better impedance value in your room system.
You have to test and evaluate with different loads till you be satisfied with.

Of course that you can contact directly to Lamm and ask their advise about.


Regards and enjoy the MUSIC NOT DISTORTIONS,
R.

For most MC cartridges, as Chakster said, any load resistance above 100 ohms will certainly "work".  People do argue about how a particular load resistance "sounds" with a particular LOMC cartridge.  If you will read the contentious thread on this subject that is still alive, you will see that most agree the load should not appreciably affect frequency response, until you get way down near the internal resistance of the cartridge itself.  You won't have that problem.  I suggest you can ignore the issue; you cannot do anything about it anyway, as your Lamm seems to use a built-in SUT to derive gain sufficient for your cartridge.  It also seems the secondaries of your built-in SUT are loaded with the 47K ohm resistor used when you connect an MM cartridge.  I am guessing that the SUT has a 1:10 turns ratio, which means it increases the output voltage of the cartridge by 10-fold, to drive that 47K resistance.  (10-fold voltage gain is the same as "20db" of gain, quoted by someone else.) Since the net resistance "seen" by the cartridge is fixed to the value obtained when 47K is divided by the square of the turns ratio (in this case, 10^2 = 100), your MC will see ~470 ohms (47K divided by 100).  You cannot change this without some surgery to your unit, and I don't recommend it. You'll be fine.

What load do you think is best?

It is interesting question.
If your phono stage has a built-in (1:10) SUT then i can tell you that i have similar phono stage from another manufacturer and it was OK with ZYX LOMC cartridges.

But the ZYX CPP-1 pre-preamp i have mentioned was better and much more impressive for the sound of my ex ZYX cartridges. ZYX CPP-1 Headamp is active device (battery powered) and connected to MM phono input.

With different MC phono stages (with optional loading like my modified JLTi or stock Gold Note PH-10) i never use 100 Ohm with MC cartridges, mostly 500, 1000 or 10 000 Ohm.

However this is personal preferences and system dependent.