Port forwarding only applies if you want to access the DNS-321 NAS from outside you network.
A second router is not really necessary. You can assign your PC a temporary static IP address in the 192.168.0.x range and connect directly to the DNS-321 in order to change its settings. You may have been lucky that the extra router war on the 192.168.0.x subnet. If it wasn't, you would have had to change the etra router's setting for this to work.
BTW, there is no rev. 1. If you have the latest red stripe Actiontec, it is a rev. I.