Redglobe,
I have two questions:
1) Is your $1600 budget for amp, preamp and phone stage? If so, I don't think you can make a significant upgrade to all three. If your amp and speakers work well together, keep them and focus on upgrading your preamp. One thing at a time. An Audible Illusions Modulus 3A with phono stage will be a huge improvement over the NAD. The Mod3A is a giant killer and comes up used for $1000-1100.
2) What tonearm do you have on the VPI? I hate to meddle in decisions as intimate as cartridge choice, but you'll get a much bigger bang for your buck if you sold the 103R and bought a
Dynavector DV-20XH. The DV-20XH is a superb sounding cartridge that mates well with the phono board in the Modulus 3A. I'm intimately familiar with this combo and it will knock your socks off. It won't require a step-up transformer like the 103R. The 103R can be a great sounding cartridge, but it requires effort to bring out its best -- like a good step-up transformer and the right tonearm. The DV-20XH will be easier to get great sound.