You can view my original home brew six thruster build here.
I originally started with four T100 Thrusters and then moved up to the vectored six Thruster configuration.
After about a year of working on and off on the six Thruster ROV and its its BBBMINI Navigation Controller I decided to switch to the BlueROV2 ROV chassis which would make the ROV lighter and smaller than my home brew HDPE chassis.
The conversion of the home brew chassis to the BlueROV2 chassis can be seen here.
Since I am using the original BlueESC T100 Thrusters there are no ESCs on the Electronics Tray as with a standard BlueROV2 which means that I have had to power the BlueESCs externally to the Electronics Tray WTC. The BlueESC Power Distribution Board is mounted to the back of the BlueROV2 Battery WTC which is located under the Electronics Tray WTC. I am now at the point of soldering the BlueESC power cables to their respective solder pads on the Power Distribution Board after which I will waterproof the Power Distribution Board.
As far as converting the OROV 2.8 to a six thruster configuration, you are in for a lot of work, probably as much work as building an original six thruster ROV chassis like I am now in the process of completing. The vectored six thruster configuration uses a RPi and a Pixhawk1 much like the OROV 2.8 Controller Board. However the RPi/Pixhawk configuration has more outputs and functionality than the OROV 2.8 Controller Board without any modifications.
Also, you need to be aware of the fact that the OROV 2.8 Controller Board power circuitry is limited to about 20 amps continuous and around 32 amps peak for brief periods. The 20 amps continuous must supply not only the thrusters but the BBB/Arduino Shield and any other component that requires power like external lights, etc. There have been hints that the OROV 2.9 Controller Board will have a higher power carrying capability.
I like the ability to tilt the onboard camera in the vertical axis without having to move the ROV vertically. The BlueROV2 Electronics Tray provides that capability just like the OROV 2.8 chassis.