I should be getting a Collider soon and am really looking forward to it.
Collider is awesome! I'm using the onboard delay/reverb effects a lot in the Pro3, as they sound really good (and can be modulated)... but for paraphonic patches, strings and pads, the Collider is a great addition. My favorites are the Shimmer and Dome reverbs.
Can the Pro 3 send out CCs from the sequencer? If so, you could modulate the parameters of the Collider as it is possible to map any of its parameters to CC numbers of your choice.
Yeah, Pro 3 can send CC data... I've went down that road before with other synths and outboard effects units - while it's technically possible, I've just found its too much work when considering sync'ing program changes and CCs for multiple patches. Perhaps if you just wanted to map something more global like reverb/delay mix levels, that might be a good option to have on tap.
I really like the Pro 3 onboard effects though, and find them very usable for most of my effects needs... It would be cool to have a reverb shimmer effect built in, and I would love it they added some more parameters to the stereo delay effect... like ping pong or alternate timed L/R delay... those are the primary things I'm gonna use Collider for.