The Sonus Faber speakers are capable of revealing tons of micro dynamics and benefit greatly from properly matched electronics AND cables. If you otherwise like your 6.1 receiver and are looking for a different sound then try some cable changes...especially if you are using Monster cables or some other generic wire. I have found that Kimber's PBJ interconnect and Audioquest's Type 4 speaker wire mate particularly well without revealing too many warts in entry level gear. You end up with reasonably high resolution, very good detail and just enough warmth to work with a broad range of music. The synergy is spread across the entire frequency range without doing anything bad.

Most High End shops will be happy to loan you cables to try in your system. Why not take advantage of the service and see if you can save some serious green for other things?

As for your receiver, yeah, you have way better speakers than that.

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I think Monty has hit it dead on and I second the Kimber interconnects. I assume your reference to "low levels" referred to volume levels rather than low frequencies and that subwoofer support isn't the issue.

Maybe you could demo an amp (if your receiver has pre-out) and give her a go. If you liked the NAD paired up with Sonus Faber at the store then that is as good a place to start as any. I would borrow another QED Tube IC to keep things as similar as possible and avoid mixing ICs.

I suspect the superior NAD amp would be a big step up in sound. It might not be the increase in power you are hearing, but the increase in electronic quality.