Sorry to revive an already [sOLVED] thread - I'm also on a Optiplex 3040 Micro, i5 6500T, HD 530, 16 Gb RAM, 256 Gb SSD - and High Sierra 10.13.2.
I've followed everything in this thread and got almost everything to work - what I've got left to solve is bluetooth and HDMI audio.
I'm getting audio from internal speakers, so that one is working - my guess is that the missing HDMI audio could be due to the fact that I'm running a Dell 3818DW-monitor (with integrated speakers) and neither HDMI nor DP gets the resolution correct (HDMI stops at 1080p, DP at 1440p).
macOS identifies the monitor correctly, but not the resolution - so I'm guessing that the identification here could be related to HDMIaudio not working.
Any suggestions for both bluetooth and HDMIaudio/screen resolution?
Thanks in advance.