Try to use NS-525F
Hi there,
Have you decide to buy the floorstander speaker?
If not, try to find floorstander Yamaha NS-525F. This is much more better than NS-777. I compare them both just before I decide to buy the speaker.
The material of NS-525F (advance PMD) is more better than NS-777 (PMD, which is used for NS-515). Look at the weight of them NS-777 (about 20lbs or 10kgs) is just half of NS-525 (about 44lbs or 22kgs). My suggestion before you decide to buy the speaker. Try to replace the AV-Receiver with at least Yamaha RXV1500 or higher, and set the crossover to the lowest (40Hz). Then LFE should be set to both front and Sub Woofer. And don't forget to set all speaker to "Large". This should be better bass and more better day by day due to break-in of all the system. For the sub-woofer, how big is your hearing room? You better compare the subwoofer YST315, YST515. I have heard all the Yamaha sub-woofer, for me the smoothest bass is YST 315

Some time more expensive is not more better.
Anyway, I agree with jcPanny to look and think about B&W speaker. Better sound with less power, even the size is much more smaller. I use them to replace all my 7.1 system. It sound much more better with the same AV receiver. Before replacing the speaker, I use Yamaha NS-525 as front. NSC-525 as center and NS-50F for side surround and NS-E55 for back surround.
Replace with B&W:602,601,600 series. It improve the sound a lot.
BTW, what kind of Player that you use to?