I'm not sure that a passive adaptor will give you the full benefit of a balanced rig. The benefit of the balanced microphone comes from differential amplification that is done by comparing the signal between pin 1 and ground and pin 2 and ground. If you simply adapt the 3 wires to 2, you lose the ability to do comparisons and reject common noise. Given the cost of a good mic, I'd buy the powered XLR adaptor that will reject noise, then feed a clean, and optionally amplified signal into the camera through the unbalanced input. As long as the wire from the adaptor to the camera is short, it won't pick up any discernible noise. The people I bought my zoom controller from (SignVideo) sell an inexpensive XLR adaptor, similar to the BeachTek, but significantly less expensive.