Is it possible on most pre-pros to route the LFE signal to the front main speakers in the case that the front L/R speakers are either very full range or have built in powered subs?
Not a good idea. First if this is a line-level output (which it typically is) you must amplify it before going to any speakers. Are you going to amplify if with the same amps that are handling your full-range signals? Nope. So you need a special amp for this. Then are you going to hook that amp up to your full-range speakers? No again.
Only if your speakers have a special LFE input can this work. The Genesis 6.1 have provisions for this, and have a built-in servo amp, but few other speakers that I know of do. Even with a dedicated input for LFE, it's far too easy to blow up a speaker from LFE signals.
Do it the right way - get a sub for LFE.
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications