I can go on and on about the idiocy of the dealers.
But, then again, the deal with a lot of different cars and they are there to follow guidelines.
Most of us are on this forum every day learning about this car and they aren't.
What I'm kind of surprised about is this comment:
"my biggest concern going the aftermarket route is that I don't want to have to deal with the maintenance on an aftermartket LSD nor voiding my powertrain warranty... "
I'm curious with what kind of maintenance you think is involved.
You replace the open dif with the LSD, and that's that.
There's nothing special that goes along with having an LSD especially the quaife, which is a non clutch LSD, which means that you don't need any special additives or anything of the sort.
The fact is that the only cars with an LSD are the M cars.
Even the BMW Z8 has an open diff.