Thank you for the information. I think you are right on since I have two of the MiniSAS HD to MiniSAS HD cables you linked in my unit. So sounds like I'd need to either purchase the right angle cables, or consider buying cards with the benefits that brings.In my TRTP+ the backplane goes to the motherboard via a MiniSAS HD to right angle MiniSAS. This uses the onboard controllers and limits the backplane to 10 SATA drives. In order to get all 12 drives and/or SAS support an optional card is required. I would guess that your chassis was purchased with that optional card but when it was sold to you the card was removed.
SM lists compatible cards as the AOC-S3008L-L8e, AOC-S3008L-L8i , or AOC-S3108L-H8iR.
Others may work but I am hesitant to say so because I noticed there is additional wire along with the data cables. I am not sure of its purpose but maybe someone else can chime in.
One further question, I'm guessing one of these MiniSAS HD cables supports 4 drives? There are four MiniSAS HD ports on the backplane so maybe that's not correct? Each one of these ports controls 3 bays?