If you examine the impedance curve of the M5, you'll notice it dips to 6 Ohms below 80Hz. It dips even lower between 100Hz and 500Hz but there's less energy in that band typically. Therefore, try cutting the M5 off at 80Hz to see if the clicking stops. If it does, that tells you all will be well when you get a sub.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated