How I work: I have a MIDI drum track I record other instruments to, and when I get into the song a bit, I'll record MIDI drums with my Yamaha keyboard. Delete the click track.
I typically use the keyboard's sounds until I get the song mostly done, and replace some or all of them with soft synths.
Recently, the keyboard stopped making sound. It still sends and receives MIDI, but no audio.
So, any song I open that I want to mess with needs to have all of the MIDI tracks rerouted to soft synths in order to hear the MIDI.
I read here that if I set the MIDI output to 'none' in Preferences, TTS-1 will automatically insert. Turned out not to be the case for my old program (unless there is some setting I'm missing).
I decided to use SID, inserting 1 instance for the kick.
I have MIDI tracks for kick, hat, snare, cymbals and toms in this project, and expected to have to insert 1 instance of SID for each MIDI track. But all of the tracks played through the single instance of SID even though each track was using a different channel and (I thought) SID was not multi-timbral.
Surprised and pleased, but how and why did this happen?
Later, on my non-DAW, I tried the same thing using the same project in X3 and it didn't work the same; I needed an SID for each MIDI track.
Strange.

Automapping w/ TTS-1 started with X3.
 
WRT CW sfz engine synths, a few have a multitimbral mode where the MIDI channel assignment matters. For example, DPro, Rapture and RPro when setup for multitimbral mode assign a channel for each element; channel 1 with element 1, channel 2 with element 2, etc. While it is possible to write sfz files with channel tags, looking at a couple of the files for SI-Drums, there are no channel tags in the files, so the synth ignores channel info.
 
I do not know why SI-Drums would act differently between the two DAWS. I can insert SI-Drums on X3 and point multiple MIDI tracks to a single instance of the synth and it will play the MIDI data regardless of the channel used for the MIDI data in the tracks..

Cool. I'll check into it more thoroughly later, but at least I know I'm not losing my mind.