Quick update on my addition of an SVS Micro 3000 to my M30.1 system.
I speak for myself in my living room with my equipment. LR is maybe 17 x 13 and I have the Harbeth's about 24" from the back wall, with the sub in between the speakers, closer to the right speaker but in the same plane as both. I think I mentioned before that I use an Innuous Zen Mk3 streaming qobuz into an MHDT Orchid DAC into a Pass INT-25 integrated which feeds the speakers and the sub. The sub is connected to the speaker outputs of the Pass by the use of a speaker to line level attenuator. Kent English from Pass helped with this solution (so did SVS tech support). I would rather have used lower level line outputs but that option was not available.
It integrates just fine :-). I played with some of the settings (volume, low pass filter, parametric EQ mainly) and came up with what I found works for me. Easy to hear a very positive difference in "palpability" of my music (mainly acoustic, old rock, jazz). The sub makes for a more "complete" performance. Depth. Bigger soundstage.
It's a fine addition to my system. I like it a lot and it was not very challenging to do by ear.