Terrence, it is rather difficult to matrix an M/S recording on a conventional mixing desk. You would have to split the outputs of both the M channel (forward-facing) and S channel (side-facing figure-8) microphones, and invert the polarity of one of the split signals from the S channel. Then you would need to mix the M signal with the non-inverted S signal to produce stereo left, and the M signal with the inverted S signal to produce stereo right.
It can be done with some difficulty, but the gains applied to the two splits from each microphone's signal must be very precisely matched (i.e. the M gain doesn't have to equal the S gain, but once you've split M, both of its halves must receive equal gain with each other and once you've split S and inverted one branch, both of its halves must also receive equal gain with each other).
All in all, I think it is more straightforward and reliable to use a dedicated M/S matrix for this function than a mixer.
You definitely have to orient the S (figure-8) mike sideways, but it's not a matter of panning. In fact the object is to mix the figure-8 with the cardioid--but then the sum is one of the two stereo output channels. The other stereo output channel is obtained by summing the same two mike signals in the same proportion with the figure-8's signal inverted in polarity. M + S = L, and M - S = R.
--best regards