Brian1965,
I'd seen that M2090 power configuration list and still find it a bit mystifying. It seems casual engineering that the M2090 has a 6-pin and 8-pin connector but that it will run on a single 6-pin or really any combination. Perhaps it matters only under extreme compute loads. At the moment, the M2090 is running on a 6-pin and an 8-pin on a 6- to 8-pin adapter. But, it's good news overall.
My expectation is that the z620 would accommodate two GPU's each requiring two supplemental power connections, but the presence of those must be a matter of the original specification of the system. My system certainly varies from yours as the power lead to the DVD drive has no other connectors. As the z620 has the two SATA power takeoffs on the motherboard- which are called internal USB connections on the motherboard diagram, I've ordered a couple of SATA power to 6-pin adapters, but it's good to know there is more than one solution. I'm looking forward to trying the K4200 + M2090 with a trial of Octane rendering.
Thanks again!
Cheers,
BambiBoomZ