SOme info on the web regarding headphone mixes in the Audiobox 1818VSL reference settings in the little mixer program that was also their interface settings app, and Presonus did away with that mixing menu app some time ago.
 
Just be aware of that when looking at any retrieved info on using headphones with that interface.  I happen to have my interface output feeding into a mixer and THEN to direct boxes and speakers, so I always just use the headphone jack on my mixer to monitor everything there - meaning no direct hardware monitoring, HOWEVER I AM getting to hear it as it exists in Sonar that way, and for ME, that works just great, as my latency when tracking is running around 5 ms each way using 128 samples for my ASIO Buffer Size.  (When mixing, I always bump that buffer size up to 2046, since latency is not an issue when playing back during mixing or mastering).
 
Bob Bone
 

Ok. I finally reconnected my old Alesis I/O 26 interface and VIOALA! The straight midi ch.s work like a champ.  So, it was the MIDI IN on the PreSonus 1818 wasn't working, which makes sense since I could see the MIDI signal going ALL the way through the cycle, incl. thru the DAW.  So, that case is solved, however, I have another issue since I installed, then UNinstalled the Bandlab version cuz it ignored all of my customizations.  NOT COMPLAINING!! Don't put me in Max Security.  Anyhoo, now my PreSonus FP-8 doesn't respond to Platinum no matter what I do.  PreSonus says their FP-8 works fine on their Platinum install.  They're still looking at my Sys Info file.  I've checked my BIOS, Windows Updates, etc, etc, etc. Any ideas. I'm also going to post this issue separately.
 
FYI, I sincerely, tried to mark this SOLVED, but I couldn't find that button anywhere.