I have a pair of NS-555's and they are still breaking in a bit, I think. They were a little harsh at first but have smoothed out over time and use becoming more natural. I am using them as my mains for my Home Theater and the room is about 12 X 14 so they are more than capable. These are ported in the back so placement by walls and corners is a selective process, the positioning changes their bass response a lot, so if you are not getting much you may try shifting them around. Also they can be Bi-Wired which is supposed to increase the bass response too. So far I am enjoying them for 2 channel music or surround sound films and music.

Yamaha makes a lot of music equipment from studio speakers to sound systems a band would use in a club. They seem to have a pretty good handle on sound reproduction and for the money often make pretty good stuff. Super audiophile? No but for the average joe they do more than a fine job at making the music real, natural and inviting plus the pod race from Star Wars sounds awesome thru mine.