What specific adaptor do I need for my Flex 6700 Balanced Microphone/Line Input

I don't know about the Pro-set 6, but I believe the PR-781 has an XLR connector. If you want to connect it to the rear balanced input, just use a standard XLR female to XLR male mike cable. Alternately, you can use a balanced XLR Female to 1/4 inch TRS (Standard 1/4" stereo headphone type) connector. The rear balanced connector is a dual-type connector that accepts both XLR and 1/4" TRS. Nice! I recommend the XLR input on the rear if you have, or can get, a standard balanced XLR cable. I am using the 1/4" TRS because I already had one made up for another rig. The front mic (8 pin) input is wired like the standard Yaesu connector.

Ken's description of the XLR cable for the 781 is correct.

I suggest you simply buy a ready made cable. They aren't expensive. If you want the details see the Wikipedia entry for XLR connector. It provides the information for each pin and even shows the XLR/phone connector used on the 6700. http://en.wikipedia.org/wiki/XLR_connector

Thanks for the leads. I am trying to connect a Heil Goldline (XLR 4) to the Flex6700 Balanced Audio using the XLR 3 jack. I searched the internet for a premade cable but didn't find one (until yesterday via DXEngineering) but by that time I had purchased the parts (about 1/2 the price of the premade cable). I am attaching a diagram of what I am doing. Even though I think I have the answer to the pin out question, I have to say that I am not 100% confident -- there are a lot of contradicting information on the pin outs on both the XLR4 & 3. I hope I have it right.

I have the connectors and cable to make up this cable to connect my Heil Goldline to my 6700. What I haven't figured out is should I connect the XLR connector shells to the shield, both ends, only one end (which one?) or neither end?