There have been some great replies about balanced systems. The noise floor is lower. I work in balanced systems only and one thing manufacturer's have cautioned about for years is to not use a combination of unbalanced and balanced. When I have to incorporate an unbalanced input into a system I use the Rane Balance Buddy. It is an unpowered device using Reisenbach transformers.
http://www.rane.com/bb22.html
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