Great tip from DGroves on the newer faster UHS-II memory card format... I did not know about that. The newer UHS-II cards are built differently but backwards compatible with UHS-I devices. Here is a good brief educational link:
https://www.electronicdesign.com/memory/whats-difference-between-sd-and-uhs-ii-memory-cards
The 19 pin plug he mentions fits in the standard "USB3 motherboard-type header" that is available at the rear of the HP "2x2" TI-chipset PCIe card I show.... it is actually a "2 x 10 header with a 1 pin blank".... very much the standard for these. If you look at the StarTech card reader you'll see a front dedicated USB3 port at the bottom right face of the reader, which runs straight to the "2x2" PCIe card in one of the 2 blue cables, and the second blue cable fed by that plug is only for the media cards. The HP USB3 media card reader I referenced uses only one of the 2 possible USB3 channels so its data cable is less bulky. The HP media card reader's cable length is perfect in the Z420 build I show, with the card reader sitting in its adapter in the lowest of the three 5.25" bays.
The PCIe card is located in the very top PCIe slot, above the PCIe x16 video card slot. The backplane port above the card is an extra..... great for locating the eSATA backplane access into.