Focusing on speaker wire length is just plain anal (and irrelevant) when in comes to answering the OP's question. Feel free to experiment with (probably class D) more powerful amps, but you may find that they don't give you significantly better (only different) sound than your NAD.
Power Amp Question
Question: how to match a power amp to my system using an integrated amp as a preamp.
System:
Triad Gold LCR In-Room Speakers 4-OHM 100-400 watt
Audio Tecnica AT-OC9XL Dual MC cartridge
NAD C356 integrated amp
Rega Aria MK3 (recently added)
Thank You
G