I'm on Yosemite 10.10.3.
I'm using this version: "RehabMan-Generic-USB3-2014-1016" corresponding the GenericUSBXHCI.kext provided by RehabMan.
With this version everything seems to work perfectly. But when using an external display through the HDMI port and an external USB audio interface, the system freezes when trying to initialize core audio inside Logic Pro X. If I disconnect the external display I can work perfectly inside Logic Pro X using the external USB audio interface.
I didn't have this issue with Mavericks. Also If I use an older version of the mentioned kext I can work inside Logic with the external display and USB audio interface, but leaving functional just one USB port.