Sorry SaturnusDJ about responding late, but my new build has been unstable, keeping me busy.
I hope the picture explains my simple workaround. The right connector is not used but it has a RPM signal (+) on the yellow wire and (-) on the black one. The left connector powers the 2 wire fan and displays the "borrowed" RPM signal.
In your case, you could possibly share the RPM signal from the 3 wire fan with the 2 wire one by interconnecting the yellow wires.
On the other hand, Okinawa Okimoto tells us hat 2 wires should work, (contradicting his college) and I see no logical reason why it should not. Just the fact, that it did not work for me
Even some 3 wire fan's would not work right away, but that was quickly solved. Don't remember exactly how. I think Kaze Server reset was not enough but a power off did it. Maybe I didn't press the reset button for 3 s. as required.
So did I miss a trick for kick-starting on 2 wires
Anyway, the Kaze Server was a great help for optimising my cooling setup.
When they deliver, I still prefer more robust solutions for control of critical fan's in daily use. That is mainboard controllers (+ speedfan) for variable and fixed voltage hacks for manual. The Kaze Server does the rest and serves as a temperature and RPM display.