The KM100 series with multiple interchangeable capsules will certainly give you additional flexibility in your choice of pattern selection. And the answer to your question about susceptibility to humidity is a resounding NO. Since your mixer does feature a switchable low frequency roll-off, the KMF module would be redundant. Complementing your current selection of 180-series models may be cost effective, and adding a bi-directional KM120 will enable you to make M/S-stereo recordings. However, have you considered the elegant solution of a RSM191A for M/S applications?