Hi Bernie
Not quite sure what you are getting at, but if I understand correctly then the following should help. (Make sure you have DFD (Disc streaming activated))
If you load Colossus into Kontakt 2 (Depending on Ram and CPU) you can play up to 16 different sounds simultaneously per Midi connection/instance. (Load 1 sound per channel. (If you use the supplied Kompakt Player you will need to load 2 instances of Colossus, as the player is limited to 8 sounds))
Also if you want to change voices while playing, just make sure you have them pre-loaded on the required channels, that way they are available immediately without any loading time. (Again the amount you can load depends on Ram, CPU and Hard Disk)
As to the vibrato, just assign the effects to the sliders/knobs on your controller and adjust them in real time until you are happy, then save it as a user voice in Kontakt 2.
Hope this helps

Bill