Happy NAD! Independent controls for each line too. Nice! I don't know much about tubes or non-tubes, but if tubes were your plan then sounds like a helluva deal!
You're not alone MKM in the discussion about Tube Amps VS Solid State. I didn't really understand it either, but my ears told me that a tube amp just sounded better. Apparently, there's some solid science as to why, and here's how I understand it.
Sound comes through an amp's circuitry / speakers as a wave. When the maximum power level of the amplifier is approached, it starts to chop the peaks off those waves which comes out as distortion. This effect is commonly called "clipping" by the technical folks. The chart below shows a visual comparison, with the solid state amp on the left, and the tube amp on the right. In a solid state (a.k.a. transistor) amp, the clipping is sudden, so the distortion comes out very harsh sounding. In a tube (a.k.a. valve) amp, the clipping is more rounded, so it sounds more natural and pleasant to the ears.
Even when the amp is not being over-driven, the clean sound coming through a tube amp has what's often described as a "warmer tone", with more dimension and harmonic range that sounds more natural to the ear. The downside is that tube amps are usually a lot more expensive than solid state amps, but a lot less power is needed to achieve a good volume level. A 15-watt tube amp will usually generate as much volume as a 75-watt solid state amp (varies by brand somewhat). Tube amps also tend to have more "personality" by brand or type of tubes being used, with each one having a different voice and characteristics that appeal to different guitarists and styles of music.
That's my "layman's amp primer" MKM, and I hope it's a bit helpful.
ACOUSTICS: Cordoba D10-CE / LaPatrie "Concert" / Takamine GD30CE-12 / Norman ST30
ELECTRICS: EP Les Paul Custom Pro / Gretsch Streamliner G2420T
AMPS: Traynor YCS50 / Peavey VK212 / Traynor AM150T
EFFECTS: Boss ME-80 Multi-effects / Ibanez WD7 wah