I finally got my TS-XL406 working!
I was getting the "ACP_STATE_FAILURE" ,
when trying to reflash the unit as it was reporting the firmware as blank.
I was able to resolve it by using Linux and presetting and formatting the 4 drives for XFS.
Then in the Debug settings unchecking to rebuild partition table.
I was then able to refresh the firmware from emergency mode and am now at version 1.20 with all 4 drives as Raid0.
Just wanted to pass this info on in case others have the same issue......
I started with just the unit, no drives and added 2: 1.5TB Seagate Drives,1: 1TB Western Digital and 1:500GB Western Digital. So I have 4134.3 GB of Network accessible storage now!
Hurray!