Sigma3 ... Did you test it with the original Mil. Spec mic in the headset?
Just asking because i have heard from one guy that his radio is doing fine with Msa Sordins Dual Comm´s and the Nexus U94 it came with ..... No impedance issues for him with the original mic he said!
On a side note ... the ICOM U94 Ptt´s have an internals Impedance matching circuit .... so if you can get hold of one and change the ICOM to U229/U it should also work with original mic´s ....
(Pic from =>NEO<= from ODA541 forum)