So my thought is....and help me here.....can we remove the plate and run risers or a softer full plate? Its such a nice ski that I know she would ski more if it wasn't as demanding.
Any thoughts or idea (outside of selling) would be helpful.
Do you mean the MX70 or the previous (nearly identical) RX70? The plates (different companies) are fairly neutral already, pretty close to straight carving plates. So IMO all you'll be doing is producing some holes to fill and spending $150 on a new similar plate and mounting.
Keep in mind that a typical plate is less about longitudinal stiffness - what we call flex - than about torsional stiffness and leverage. A plate helps prevent the center of the ski from twisting like a dishrag in a hard turn, and it makes getting on edge easier, less force required. But if a ski feels "too stiff" that's typically the construction of the ski itself, all the way out to the tip and tail.
Now some World Cup plate are long enough and linked in a way that they will add significantly to the ski's middle longitudinal stiffness, but the MX/RX70's Tyrolia/Marker plate is nothing like a WC plate. Incidentally, the middle of a ski where the plate is rarely bends anyway, unless the skier has the ski under serious loads and way over on edge. Consider that the boot sole itself is part of the system, and boot soles don't tend to bend much.
What length MX/RX70, and what size is your fiancee?
I owned the earlier incarnation of this ski. It's not particularly beefy or demanding; I'd rate it roughly 2/3 of the way on a easiest to toughest scale. Like all Kastle's, it prefers to be driven rather than ridden, and gets easier with velocity, but it won't punish transgressions like some skis. So if your fiancee's size is a decent match for the ski length, I'd suggest that you guys spend the $150 on a couple of lessons. She'll discover it's a precise, smooth premium ski that will grow with her.
Hi - You have exactly the right length for her, and that's a fine ski. The RX70 plate was made by Marker (have roughly similar one on my RX12's), and has been rightly praised by binding specialists here like Phil as being the best out there at being invisible, not interfering with the feel of the ski or its flex. All plates extend out beyond the binding footprint, so makes sense why you were curious, but naw, not an issue here unless she has extraordinarily large boots for someone her height.
I'd guess that it's a combination of the ski sidecut design and the driver. The RX had a dual radius design, with the shorter curve in front. So it would dive right into the turn, but feel a touch less helpful at the end. The solution is to stay on the edges through all the turn. The tail has a really nice progressive flex, lot like a Stockli, so it won't have that "load and throw" feeling that some love and some hate, and will be very predictable. But a lot of decent skiers (speaking from personal experience here) tend to hurry the end of the turn, because they're really focused on the start of the next, especially in steep terrain. The MX tail wants her to really cross the t and dot the i's, trust the ski to finish and be ready for the start of the next. If she doesn't, the tail will tend to feel like it has its own agenda. If she does, it will load, smoothly, and get her into the next turn quicker than she expects.
Cue: "Gotta have faith…"