Your NAD receiver has plenty of power...more than many competing receivers out there. What may have you confused is that your NAD receiver is "only" rated at 80 Watts/channel, while you probably see 100+ Watt/channel ratings all over the place. The thing is, there is no standard for rating amplifier power. It is basically possible to "cook" the numbers to make whatever figure the marketing department would like!
Your NAD receiver is extremely conservatively rated if you go by the common practices of other major brands. Your NAD's "80 Watts/channel" would likely be rated as "280 Watts/channel" by several other major brand name manufacturers!
It's also important to know that in an anechoic chamber, you need twice as much power just to raise the output by 3 dB. But in a real room, you only need 25-50% more power. Another way to look at it is that even if you were comparing 80 Watts/channel vs. 100 Watts/channel - with both ratings measured in exactly the same way - in real world terms, you'd only be gaining 1-2 dB of extra output from those 20 extra Watts.
Bottom line - do not get hung up on Watt ratings. What is important is whether or not your receiver has a strong power supply and a good design. Your NAD does. And you are better equipped to drive lower impedance and/or less efficient speakers than most people!
If you are after full THX spec loudness levels in your room, then yes, you will still need very efficient speakers. But very few people actually listen at an average 85 dB volume level with 105 dB peaks! Most people prefer a good 10 dB quieter, which, in a real room, means you need about 15-20x less power than if you were reaching full THX spec volume levels.
The other factor is how far you are sitting from your speakers. For every doubling of the distance, you need 3 dB more output and about 1.5x as much power in order for it to subjectively sound about equal in loudness. In other words, if you're sitting 10 feet from your speakers, you'd need about 1.5x more power if you moved back to 20 feet from your speakers in order to maintain the same subjective loudness.
All of that said, efficient speakers are almost never a bad thing. Efficient speakers are more dynamic and can more easily provide sudden loud bursts and prolonged loud passages. For you personally, though, you really do not need to worry. So long as you do not select especially inefficient speakers, you'll be just fine
There are many great brands out there. For your room size and listening desires, I would heartily recommend that you check out Axiom Audio. Axiom produces excellent, dynamic and accurate speakers for reasonable prices. They would mate very well with your NAD receiver, provide the kind of output and dynamics that could fill your room and also do very well with music, thanks to their accurate and detailed sound qualities.
