More power or better quality power?

I am researching new integrateds because my System sounds lifeless.

Sonus Fabers lower models need an upfront and dynamic amp or else it would sound as what you've described. Also, since you listen to mostly rock, you would certainly need to look at the amp. Primare and Plinius are not good choices are they are on the lush and warmer side of things. I would suggest a Krell integrated. If possible, try to borrow a KAV-300i and see what it will do in your system. It brought back life and dynamics to my Grand Pianos which sounded like dead speakers with my Plinius amp prior to auditioning the Krell.

I have owned Sonus Fabers before and share your same thoughts. Although I still can make them work, I chose to get rid of the speakers and find some new speakers that are more neautral. It's your call on whether to work on the amp, or the speakers.

If I were you, I would look at the amp first cos your current NAD is on the low-end. If you upgrade to better speakers the NAD won't do justice to them and it's back to square one.

Ohh yes I guess those tube guys don't care about neutrality anyway as they continue to roll their tubes...

I do believe that if one amp/preamp sounds substantially different when level matched operating within their linear region, then one of them is broken (possibly by design).

In my opinion, I don't believe one design is broken if it does not sound the same as with another design. Speaking out of common sense, all designs, be it amps or speakers are all different. The parts inside the amps, the type of parts, the arrangement of electronic boards etc. are all different and that explains to why they sound different. In general/theory, an amp is supposed to be neutral, in fact everything should be designed close to as neutral possible so as to reproduce the signals in their true state. This doesn't appear to be true in actual case. Designer's may be striving to achieve neutrality but most equipment more or less have their own kind of sound due to the points as mentioned above. The term is subjective and debatable. In fact, I don't know how we can classify any particular equipment as neutral. Only if we can measure neutrality.

More technical persons would be able to explain or clarify in better terms.

In response to the poster of this thread, it would be good to get a quality integrated amp as opposed to using your NAD as a line stage in the long run.