On page 29 of the Darwin (uh, I assume 1.0) manual, under the heading "How it all works" in the section "Synchronizing with a sequencer"...
DARWIN and the sequencer are both controlled by the sequencer transport controls. When you press PLAY, the sequencer puts itself into play, but waits for the external clock. The MMC Play command is simultaneously sent out to DARWIN. On receiving the MMC Play command, DARWIN begins playing and sends MIDI Time Code back to the sequencer which starts and tracks in perfect synchronization.
So... it would seem that it's the sequencer transport controls you would work with, not the ones on the DARWIN. Remember to set the sequencer clock source to external on the sampler's sequencer. Turn on MTC Out in Darwin, and set MMC Mode to Closed Loop (meaning you have the sequencer MIDI In and Out connected to the Darwin MIDI Out and In respectively... you must connect both... it's not necessarily the brightest design, but I'm sure the MIDI committee thought it was a good idea at the time).
*Note: No guarantees implied or offered. I'm just sussing this from the manual, as I have never actually encountered the Darwin hardware (although I did see two systems up for sale in one week on eBay back last year).