This answer was previously the question, and the question here was actually answer.
Wow! This program is complex for my level of understanding! Finally got midi to record and play back after reading Studio One 3 : Global and Focus MIDI Mapping in the Knowledge Base 'New Features' section. I also had to place the device (Roland DR-5) in Song mode to allow the iMac clock to synch and control. Lastly, it also helped to widen (pull down) the track from the default setting to view options that were previously hidden. Sweet!
Mac, (Retina 4K, 21.5-inch, Late 2015) OS X El Capitan v.10.11.2, 3.1 GHz Intel Core i5, 8 GB 1867 MHz DDR3, Intel Iris Pro Graphics 6200 1536 MB, PreSonus AudioBox iTwo, PreSonus StudioOne 3 Artist v.184.108.40.206191