'dual band' usually pertains to IR sensors / demodulators. Many IR protocols use a carrier frequency somewhere in the 34KHz to 36KHz range, but then there is a leap to 56KHz. The IR receivers usually have a sharp notch filter around their centre frequency, and are carrier frequency specific. However, the notch isn't so sharp that adjacent carrier frequencies ( such as 34KHz vs 36KHz are drastically affected. 'Dual Band' in a repeater usually means there are 2 discrete receivers, One for the 3xKHz range, and the other for the 56KHz range.
Different IR protocols use different carrier frequencies. The JP1 folks have a great deal of accumulated knowledge / data, I suggest you visit their site / forums to dig deeper. http://www.hifi-remote.com/forums/