Hi BJB,
QNAP offers many 4 & 6 bay NAS with PCIe slot for 10GbE expansion. You can consider TS-464, TS-664, TS-473A, TS-673A. They also offer optional QuTS hero for installation. Hybrid Backup Sync can support backup between 2 NAS with file-level Backup or Sync jobs if using QTS on the destination NAS.
https://www.qnap.com/en/product/compare?products=ts-464,ts-664,ts-473a,ts-673a&ref=product_overview