Studio One and iMac not recognizing StudioLive 16.4.2 as audio device (despite recognition in Uiversal Control)

Just got an iMac (Nov 2012 version) with fresh install of IOS High Sierra to use as my music computer, specs are as follows:

Computer:
iMac (21.5 inch, Late 2012)
Processor: 2.7GHz Intel Core i5
Memory: 8GB 1600 MHz DDR3
Graphics NVIDIA GeForce GT 640M 512MB
OS: High Sierra V10.13.1

Hardware:
Presonus StudioLive 16.4.2
Presonus FireStudio Project

Setup:
StudioLive mixer is connected to the iMac via Firewire 400-800 cable to official apple thunderbolt-to-firewire 800 adapter. Now, here is where it gets interesting. I would like to daisy chain my FireStudio Project with the StudioLive, so I have a Firewire 400 cable running from the FireStudio Project to the other StudioLive Firewire port. Universal control (latest version) recognizes BOTH units and stacks them the way I would expect. However, when I open Studio One 3 (latest version), ONLY the FireStudio shows up in the audio devices menu. When I go into my utilities, both the StudioLive and FireStudio Project show up under hardware. When I go into my Midi/Audio settings, ONLY the FireStudio Project shows up as an audio device.

In short, I know my StudioLive is talking to the computer, otherwise the FireStudio Project would not show up in Studio One or Universal Control, and the StudioLive would not show up in Universal Control. Any idea how to resolve this? It appears both the iMac midi/audio controls and Studio One 3 do not recognize the StudioLive as an audio device, even though it comes up in Universal Control.

My ideal set up would be to have StudioLive be the workhorse and primary audio device with its 16 inputs, with the  daisy-chained FireStudio providing an additional 8 inputs for a total of 24 inputs. As of now only the FireStudio Project, routed indirectly to the computer through my StudioLive, shows up in Studio One. Despite this I can record from the FireStudio (but not the StudioLive). Another lesser question: I have also read that connecting the units via SPDIF will minimize latency - is this true? What is the best way to do this?

Thank you in advance,
Dave

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