Smokey,
You don't need an impedience matching transformer. All you need is an adapter cable and you're in business. Email Uncle Dave, Donny Pesce, and any of the other 3000 owners who sing and they'll be more than happy to fill you in on the details. I no longer use a handheld, but when I have friends over and they want to sing through the keyboard's processor, I plug in a Sennheiser E-855 and it works just fine. Donny Pesce used the same mic for years with no problems, no matching transformer, just an inexpensive adapter cable.
Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)