What networking expansion does the Synology DS923+ offer?

Regarding the Synology: The DS923+ includes a PCIe Gen3 x2 slot for adding a 10GbE or 25GbE network card, which is narrower than the x8 slots on the DS1621+ and DS1821+ but still massively faster than the built-in two 1GbE RJ-45 ports for large file transfers.