Topic: UFX USB cable lenght?

I would like to use a longer USB cable on my UFX to my win 7 64 computer, say like 15 feet or even longer.
How long of a cable will work and be supported by RME? What about active USB cable extenders?

i7 Extreme 990X 3.47Ghz, 24GB RAM, Fireface UFX
Nuendo 8, Halion 6, Wavelab 9.5, Izotope RX 6