Jafreeman, the issue here is that if you put signal (ground) current through the shield, you can wind up with undesirable effects. In a balanced cable, the signal should only appear between pin2 (non-inverted) and pin3 (inverted) of the XLR. IOW ground should be ignored.
Quite often in high end audio the tenants of the paragraph above get ignored. The result is really expensive cables, or a lot of work put into the cables for no real benefit. If you run separate shields, you will loose a lot of the Common Mode Refection Ratio afforded at the input to the amplifier! IOW use a common shield- it will work better- noise gets into the cable, you **want** it to affect the inverted and non-inverted phases equally! If this does not happen the cable could well have more noise.
Quite often in high end audio the tenants of the paragraph above get ignored. The result is really expensive cables, or a lot of work put into the cables for no real benefit. If you run separate shields, you will loose a lot of the Common Mode Refection Ratio afforded at the input to the amplifier! IOW use a common shield- it will work better- noise gets into the cable, you **want** it to affect the inverted and non-inverted phases equally! If this does not happen the cable could well have more noise.