Thanks for the reply Shellhy,
First of all, my apologies for the lateness in getting back to you.
With respect to your question, as I had a DSL connection prior to my NBN installation, I currently do not have access to a BYO router that is compatible with the NBN (a modem/router with a WAN port). I may be able to obtain one from a friend however and will keep you updated on whether or not that has rectified the issue.
In regards to connecting a computer directly to the Uni-D port, I can confirm that it is a modem issue as I am able to browse the internet without disruptions via this method. (I was previously unaware that it was possible to connect to the internet directly through the Uni-D port, so now have a temporary solution whilst experiencing disruptions.)
I am beginning to believe that it may be a technical fault with my particular modem/router, and not a firmware issue, given that other people with the same model don't seem to be experiencing the same issues, so I'll be making contact with Tech Support in this regard.
Thanks again for the reply and I'll keep you updated on the situation.