Using such radically different mics to form an MS array is never going to give great
results -- the stereo imaging will tend to be rather variable and frequency-dependent.
But for experimental purposes I'd suggest using the U87 in fig-8 mode for the Side
mic and either the SM7 or M3 as the centre Mid mic.
All you need to create a
mid-side file is allocate the mic mic to channel 1 and the side mic to channel 2, and
record as a stereo file.
However, you should also ensure that the in-phase side
(front) of the U87 faces to the left of the sound stage (as viewed from behing the mic
array looking at the sound sources). You should also set the preamp channel gains to
provide a similar sensitivity for both mics.
The easiest way to do that is to
decide where you want the nominal left hand edge of the stereo pickup area to be, then get
an assistant to stand there making a fairly constant noise (humming, for example). Adjust
the gain of the two preamp channels to give roughly equal output from both mics.
-------------------- Technical Editor, Sound On Sound