As an update; Transfer speed was due to a failing drive in the "array", which was not identified via scanner. I have since replaced the drive, re-installed the OS and Stablebit Software, and recreated the pool from scratch.
Which brings me to another issue; Scanner is not reading S.M.A.R.T. attributes. They are accessible by every other application I've tried, enabled in the bios, etc.
message shows; "The on-disk S.M.A.R.T. check is not accessible on any of your disks. Drive temperature and mechanical operating parameters are not available and will not be monitored."
I've done all the basic trouble shooting, and other drive diagnostic applications can read the s.m.a.r.t. attributes. The controller has been tested in another system in a different configuration, and I also replaced the controller to see if that was the issue. It is not likely.
Edit; I set 'Smart_NoWmi' to True in the config file (after renaming per the wiki instructions), and now the GUI won't connect to the service. I've tried saving in both UTF-8 and ASCII. Same issue.
Sigh.
Edit 2; Combing through similar threads I came across your Direct I/O tool, and I can retrieve a response using the SCSIPassthrough48 method with Unsafe Direct I/O unchecked.
Checking Unsafe Direct I/O reports as well, but... what is Unsafe exactly about this setting? The wiki describes it but does not go into data corruption, etc. I assume that since it worked in the diagnostics tool without crashing anything, that it is generally safe to use?