I do have an Octatrack, it’s very under-utilised at the moment though. I sequence all my gear from the Monomachine, and I can do most of the same MIDI stuff the OT can in that regard - apart from conditional trigs, uneven track lengths, and having two fewer MIDI tracks.
In general though, a big part of what I like about the TR-8 is how fast the sequencer is to work with, so I’ve tended not to get too deep into that, but I have played with MIDI CC from the Monomachine - especially LFOs on things like hi-hat decay and velocity. The CC implementation on the TR-8 is really good (it’s always lacked a CC for pattern change though, as does the TR-8S).
The TR-8S does alleviate a lot of the limitations that external sequencing deals with on the TR-8, eg the small number of available patterns, differing track lengths, LFO & motion control, etc., but no doubt the potential for melding crazy Elektron sequencer tricks with the TR-8S sound engine is huge. Would be great to put some time into exploring that specifically.