The controllers are of course, ASMedia products, and when used in conjunction with the bundled “ASUS USB 3.1 Boost” utility, can push transfer rates upward of the usual.
The mainboards that do support USB 3.1 exists through the tiers, and we shall just list them: X99-Pro/USB 3.1, X99-A/USB 3.1 (Transfer Express), X99-A/USB 3.1, X99-E WS/USB 3.1, Z97-Deluxe/USB 3.1, Z97-Pro (Wi-Fi ac)/USB 3.1, Z97-A/USB 3.1, Z97-E/USB 3.1, Z97-K/USB3.1, Sabertooth Z97 Mark 1/USB 3.1, Sabertooth Z97 Mark 2/USB 3.1, B85M-G Plus/USB 3.1 and B85-Plus/USB 3.1. The availability of each, however, appears to be subject to your locality.
Some of these models have on-board USB 3.1 controllers, whereas others are simply bundled with the add-on card and a BIOS update. We recommend PC shoppers to take a look at this table provided by ASUS before taking the plunge: