The "electret" mike will fix the problem. ...... so will putting an amp on the M87 ... an impedance matching transformer is only for the earpieces (phones) and would only be necessary if they were of 8 ohm (military) impedance instead of the 300-700 ohm (civil) earpieces that are prob fitted to the h'set.
Go see the folks thet sold you the set in the first place!
Cheers
