T7920 problems with thunderbolt 3 and booting disks

I have been having lots of fun trying to get thunderbolt 3 up and running on a Precision Workstation T7920.

It began with trying to find out which thunderbolt 3 PCIE card was appropriate, and if

a GPIO cable was necessary. Dell sales and technical support was not helpful, and internet

forums and the rest were not clear.

I purchased a P1XY1 thunderbolt 3 pcie card, and installed in my T7920 with the displayport

interconnect between my graphics card and the P1XY1 displayport connector. No GPIO cable.

When I went into BIOS- the thunderbolt support enable options with security levels

showed up- but I could not see any options related to booting with thunderbolt 3,

despite the fact that the panel for these options had explanatory text documenting

these booting-related options.

The board and thunderbolt support showed up in device manager, and a thunderbolt SSD as well as

a thunderbolt dock(Caldigit TS3 plus) were properly integrated- the SSD showed up as a drive and

the ports on the dock were usable.

When I connect the thunderbolt SSD that had a bootable windows system, and bought the system

up, it did not show up in the bootable devices list. This very same drive will successfully boot through

thunderbolt 3 on a Dell Precision 7530 laptop.

I would appreciate it if someone could explain to me how I can the thunderbolt attached storage 

booting support up and running.