The manual says that you should not use a cord more than 3m (i'm assuming they mean meters) In just about every scenario, I would hook up shotgut mikes with a cord thats at lease 5 to six feet long. In some cases much longer. Is audio comprimised when using longer cords for xlr mics?

You can use XLR cables as long as you want. That part of the manual must have lost something in the translation from Japanese. It's been mentioned numerous times around here.

Yeah, that's three miles - apparently that much cable weighs enough to break the socket.

(Snark)

Run as much as you need, no problems. I've run a hundred and feety feet before.

Cable length would not be much of an issue form an electrical standpoint. 3 M is almost 10 feet. Realistically you can go many 10s of feet without any electrical issues. Mechanical issues of managing long cables are the larger issue.