We use 25 foot usb/hmdi cables with repeaters on our DK2, no issues whatsoever. We do use a DVI to hdmi adapter right at the PC.
Here's links to the cables we use:
USB:
https://www.amazon.com/C2G-Cables-Go.../dp/B00B3329AW
The usb cable has its' own built in adapter. The HDMI is a regular 25' HDMI and we purchased a repeater...
HDMI repeater:
https://www.amazon.com/Tripp-Lite-Eq.../dp/B000N5YF9Y
We do not have to provide external power for the hdmi repeater.