I have used the Heil mic for the Icom, I get great audio reports from it.
I have used a D104 on a 706MKIIG, and got nothing but bad audio reports. At first I didnt believe them so we hooked the mic up to a friends 706 and I went mobile,,,,,,,,WOW THAT SOUNDS LIKE CRAP.
Heard a guy on 2 meter FM, had the Astatic 575 hand mic on his 706 and he sounded terrible! Very tinny and over modulated.
These "power mics" are not designed for modern ham rigs IMO. I know I know,,,,everyone here has used them and they have been "TOLD" they sound good and are "BLOWIN SMOKE!!" on 11 meter,,,,,,RIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIGHT
I would stick with a Heil hand mic for the Icom or get the Icom desk mic SM-20