Hey dont
We're trying to help. The ongoing conversations you are trying to have with your NTL region are something only you can pursue, and unfortunately don't seem to be having too much luck.
If money is not a problem, I think most here would recommend you went for a wireless network rather than a second SACM, it allows more flexible sharing of printers, files etc, doesn't cause problems when you want to move a PC to another room or different corner of the same room, if you game, then friends with wireless can come round and patch in without difficulty to play against you with virtually 0 lag, and if either of you have a laptop, then use in the back garden, in front of the TV, wherever is a great benefit.
I certainly would not want a second SACM, just more NTL cables and hardware to go wrong.
The gaming pack which allocates a second IP address gives equal cabling and allows both of you to use the same SACM.
A corporation when connecting to the internet does not connect each indiviual computer to the net, but to a router and that connects to the net, this is best practice. I guess this is why we are all recommending what would be considered best practice, and permitted by NTL.
Modern routers pretty much self configure, especially the wireless ones, this should be a saturday morning plug and pray excercise, rather than waiting for NTL missed appointments, destruction of front walls and damaged plasterwork.
Good luck whichever way you choose.