I've been doing some experimenting with PR8. I've made it so that instead of a counter to advance the step sequencer, it can sit and wait for a button press on controller 2.
I'm just thinking out loud here but wouldn't it be pretty simple to rig up a MIDI->electronic pulse cable and then in your external sequencer, assign a MIDI control to send each time you'd like PR8's sequencer to advance a step and it should just work?
I guess you'd have to create a "dummy" track in your song that just sent out constant MIDI messages to keep PR8 moving but that wouldn't be too much trouble would it? You'd also have the advantage of it staying perfectly in sync with your tempo changes.
Not sure about the difference in resolution. I'm still only polling the second controller port @ 60hz but unless you've got an insanely fast track it should keep up shouldn't it?
Just want to use this thread as a place for ideas as I really need to get this external sync lark sorted, for Pulsar too.