Take my gpu's sound support. If I run sound through DisplayPort it runs 40% slower and an octave an a half lower pitch. Over HDMI it runs fine. Oddly, if I have an HDMI device attached sound over DisplayPort runs fine, until the HDMI connection or computer goes to sleep.
My solution ended up being to get a cheap usb sound adapter and skip the gpu audio. As the HDMI would only do 4k at 30hz and DP does 4k at 60hz.