cyberman, Did you mean a Thecus model N5200 and not 5100?
I have a Thecus N5200 RouStor, also with 5 x 400GB 7200RPM HDDs (Seagate Barracuda 7200.8 ST3400832AS, 400GiB, SATA 1, 8 MiB buffer) running solo off an older model APC Backups 400. Seems to work ok, but I don't know how many minutes I'd get of backup time. Mostly I just wanted the AC power conditioned. I also didn't try plugging in the UPS's serial port to the N5200's serial port. Does the N5200 even support serial/usb communications to anybody's model of UPS?