Re: Hi from Spokane Valley Washington!
Hello and welcome to the addiction, er, family
The Zensor series really is a fun speaker, nice and warm, not too much emphasis in any one area. The Sierra 2 would give you much, much better accuracy and detail retrieval. The tweeter on the Zensor can't really compare to the RAAL tweeter in the Sierra 2. You'll also get much tighter and accurate bass, so much so that it'll startle you how different it can sound at times, especially complex drum work.
The NAD is great for desktop speakers and high sensitivity speakers, but isn't the best pairing for either the Zensor 1 or the Sierra-2 since they are both around 86 db @ 2.3 v / 1 m. You'd be better served by an amp that has around 100 watts of power or more, especially if you sit further back than a few feet from them. In a nearfield desktop setup you might be fine, but at loud volumes it will start to sound compressed.
You should also consider adding a subwoofer, such as a Rythmik F12 or L12.
-Alex
PS4/Nvidia Shield --> Emotiva XMC-1 --> Emotiva XPA-5 --> Ascend Acoustics Sierra Towers and Horizon Center w/ RAAL tweeters (L/C/R), HTM-200 SE (Surrounds), 2x Rythmik F12 subwoofers