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

Who said "people" can't hear differences due to loading an MC cartridge?  Speaking for myself, I simply advised the OP that the fixed loading afforded by his particular phono stage would be fine.  He has no other choice without spending many $$$.  Also speaking for myself, I have been using 47K with two of my LOMC cartridges (ZYX Universe and Koetsu Urushi), but two of my phono stages do not easily permit it.  (I have 3 phono stages in rotation using two entirely different systems.) In my additional experience, loads down to about 1000 ohms for those two LOMCs seemed a bit superior to lower resistive loads.  After that, anything down to 100 ohms will certainly do OK. When the load R gets lower than about ~10X the internal resistance of the cartridge, SQ starts to get dull (a subjective impression) and gain is measurably lost (a fact), because some signal voltage is lost to ground.  But the OP did not ask about any of this.

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.