Want to point out that this is Stoverski3's FIRST post. Welcome to EPIC!
Stoverski3, both of these guys are excellent skiers and respected members of the EPIC community; obviously they're showing some history here. Not sure they'd agree on the time of day right now.
No experience with Lines, but I've skied some TT in the same rough range as the P90 (Mojo90, Karma, Mantra 94, Scratch's, PR) and some traditional tailed in that area (K2 Outlaw, Legend 8800, Elan 777). IMO, the vaguer/softer release of TT tails makes them easier to handle in most soft conditions, and a lot of folks prefer them for bumps/trees (as long as you don't hook the tails). That said, even the firmer ones like the Karma (and I've heard that Lines and Atomics do well on hard), still don't have the bite or precision on hardpack of a traditional tailed ski. They'll have a lower speed limit. They also tend to lack the pop out of the turn that some race-trained skiers like.
This isn't a personal bias - I own and like both kinds - just basic engineering. When someone here says that he/she can rock at high speed on hardpack in their TT's, or smear beautifully in deep bumpy chop on their stiff flat tails, they're really talking about their abilities, not the innate characteristics of the ski.
So when I read your post, I see that you're concerned about chatter, about managing edges, about getting bucked, and about a ski that can handle hardpack/groomed between infrequent powder.
It would help if you specified your size and weight, but from your statement, my guess is - unless you hit the park - that you'd benefit from a damp/mid-flex traditional tailed ski in the high 70's to middle 80's. Yes, a P90 would probably meet many of your needs, and a Mojo or PE might be as good or better. But not sure these are the best choice for what sound like predominately hard conditions and your issues with edge control and chattering (if you really really want to stick with a TT, think about Fischer, which are light and damp, but legendary for bite).
And FWIW, I've been skiing for a half century, still find that lessons and good boots can help more than new skis.