So I switched out and tried the analog cables and it still didn't work right off the bat. Had to check some more channels in audio pref to get all the sound that I wanted. (Sorry, should have mentioned I have Z-5450's 5.1) Everything seems to be working fine now though. So for a summary, I'm now running them on analog with all six speakers working just fine. Thanks for the help guys.
i7 6700K - Z170 - 16GiB DDR4 - GTX 980 Ti - 512GB SSD - 256GB SSD - 500GB SSD - 3TB HDD- 24" IPS - Win10 Pro x64
2015 13" rMBP El Capitan