Got it.
The NIC might fit in the PCIe m.2 adapter and clear the panel that is the top of the case when closed. I think it would, but I don’t have an HL8, so can’t really tell definitively from the pictures. You can go janky and use an m.2 extension cable to mount the NIC to the other side of the PCIe card;
https://www.amazon.com/Extension-Cable-Extender-PCIe3-0-Speed/dp/B089YPXMNQ/ref=sr_1_9
But at that point, although still cheaper than the QNAP card, the QNAP card might be the more stable and reliable solution. There aren’t many all-in-one options that compete with it. I guess the choice depends on how important the second NIC requirement is to you.