How do you "run 5 pairs"? Do you simply twist all 5 wires together and stick them into one terminal or do you run the + to speaker 1 and the - of speaker 1 to the + of speaker 2 etc?
If you want to do a set-up like that right, you should look into a speaker switch box. It's been years since I looked into one, but Niles used to make a decent, inexpensive speaker box.
If you're going to drive 5 parallel pairs of speakers out of an amp designed to drive 2, don't be surprised if it fries. If you've been doing that for 15 years with your NAD, it definitely makes sense to bring that amp into a service shop and get it fixed. It's a good one.
The pairs of wires are twisted together. This was all professionally installed by Audio Emporium, THE high end audio store in the Milwaukee area.