I tried to make a faux LMC from scratch, and failed successfully.
I tried to emulate an SSL listen mic compressor on a stereo drum file without the SSL LMC+ plugin, and did a pretty poor job of it, but accidentally discovered a sidechain compression technique in the process. The technique added a huge crack to the snare, punch to the kick, and life to the whole kit, beyond what typical parallel compression might offer. This wasn't my aim, but it was the result. It didn't quite add the same amount of grit and character that the LMC+ does (and so my experiment failed), but I liked the result quite a bit better anyway. I'd like to share the technique. I have a screenshot with all the settings, levels, and parameters shown, but I'm not sure how to share an image here. The gist is (with a lot of details left out) I had the same stereo drum track duplicated, or routed out to 2 sends-- just make a copy of it in some manner. Pull the fader down on the copy and have it feed the sidechain of an SSL G Bus compressor (pre-fader, 0dB) with with attack around 30 and release at 0.3, aiming for 4 to 8dB gain reduction, and have that copy HPF'd so that your kicks hit around 4dB and snares at 6 to 8. Here's where it gets funky. On the copy, first create a custom reverb that sounds kind of like a control room, mixed maybe 35 - 40%. Then add another reverb that simulates a live room, mixed 65-85%. (these are out of order, my first mistake). Your shorter tail should precede the longer one. Now it gets funkier (and this is where I deviated from the experiment and just got creative with it). Slap on a distressor at 6 to 1 hitting the yellow and adjust the release until the snare starts to really crack hard. Then follow up with a dbx160 and pull back on the threshold a bit, and the compression too, until you hit about 10dB reduction. Adjust the makeup as needed (on the dbx) so that the G Bus comp is hitting that mark again. Mix the G bus compressor anywhere from 50-80% until you coax as much power out of the snare as you'd like. Adjust your makeup on the faux LMC until it's back to level.