All Lamm phonos use shunted SUT circuits for MC. So we are SUT-ing by default. On order you can specify the ratios for the LP2s and LP2.1s. The Signature has a low and high ratio.
Of all the externals I've tried the only one that gave the Lamm custom Jenzens a fight were Silvercore. In any case, if one does want to try, both models have excellent MM inputs. The tough part is finding the right cables to use with external SUTs. I use Masterbuilt (obviously)
I have tried several SUT in the $1-$2K range on my LP2.1 but keep coming back to the internal MC input. I have several classic MM cartridges (AT, Shure, Grace) and can confirm that the MM input is by far the best I've had in my system.