Waves UM225/226 and surround producing

[Harry_HH]

I consider making a couple of small 5.1 productions. Noticed the UM 225/226 is on sale again. These plugins are intended in to converting multichannel surround from the stereo information. I'd like to know how/when people are using the plugins - when you originally plan your production to be 5.1, you don't need this kind of stereo->multichannel conversion - or are you using UM also in creating separate parts/tracks before the mix and spreading e.g. one instrument (stereo) info to multichannel? H.