I own a 743 in my family room HT and have used it many times and quite successfully in many a HT designs/installs I've done. Most recently replacing someone's THX certified Pioneer receiver. But like JCD said, it's in the "ear" of the beholder. NAD amps are VERY clean and can pound!
Don't worry about "sensitivity" with NAD products, I've run them with highly unefficient speakers (low 80's) and they work like magic.
I have access to almost every product out there...why do I choose NAD 90% of the time? Musicality...while NAD does not have the bells and whistles of other manufacturers...it puts the $$$ into the parts that count. The amp does not colour the sound, but just represents it as is. Compared to a Panny or Yamaha amp...it will sound "I hate this term," more laid back. But IMHO those other amps are more (another term I hate but folks understand) forward sounding, so depending on what sound YOU LIKE, go that direction.
Amps will sound differently with different speakers...so match according to your tastes. There is a point of diminishing returns as well. Buying a pair of little bookshelf speakers costing $500/pair and matching them with a $20,000 amp...IMHO makes NO SENSE! So again as JCD said, given your equipment you may or may not hear any differences.
BTW...$400 for a warrantied T743 is a GREAT PRICE! I'd jump all over that one!!!
