Yes, that's the theory for SX. It's manual says it's a bad MIDI clock master.
In practice this doesn't work with SFP devices: their timing jumps around, generating pops and clicks. You don't want this
A sample-accurate sync for sequencers and modulation can be made by recording a Flexor ramp or mod signal to an audio track and feed it back from SX to the modular - I'm sorry, modular is not supported under XTC mode.
SFP midi clocks don't sync well to Cubase, so it's practically unusable. Best thing is to set them to internal clock...
Enjoy
