It's T-Racks' Bus Compressor for me - the SSL quad comp model. I've never heard the hardware so I've got no idea how close it is, but I love it on the master bus, usually 1.5:1 ratio, attack 1 or 3ms, release on auto and doing between 2-4dB when things are in full flight.
But here's the thing that maybe marks me out as crazy; I use it in linked M/S mode, which I think sounds wider and does a better job of controlling the groove in the centre. In L+R mode it makes things a little narrower to me, which I've heard as a common complaint of software 2 bus compressor.
Other than a hardware FMR RNC (which was ok) years ago the only other comp I've really used successfully for this job is the @bozmillar +10dB Compex - absolutely brilliant comp, but it's my go-to drum bus comp and I have this weird aversion to using the same comp on drum and master bus since it's gonna be the drums hitting them both hardest anyway, usually.