Using almost any DAW as a mixer in a live sound re-enforcement gig, latency is going to come into play. If you are not down pretty low, it's an issue. And if for some reason your computer crashes...............hope you can do comedy well with a really loud voice until everything is up and running again.

 

what about massive standalaone or kontakt player.
There isn't much you can't reproduce in either of these. Though it would take some time and sound production knowledge to recreate the patches you want from other VSTs. Though if you made a list I'd be happy to have a crack at it for you. I'm sure I wouldn't be the only one either.
Would be lighter on CPU
Strange that Live doesn't like some VSTs. are you attempting to bridge 32bit plugins?