I think the 4B Cubed is a hell of an amp, and a sleeper in the high-end. It won't give you all the tactility and liquidity of the best Class A/tube stuff, but it gets you 90% of the way there with indestructible build quality few in the high-end can touch, and of course that incredible warranty and support. It's not cheap, but one of the best values on the market in the grand scheme of things. I returned the review unit and often regret not having kept it. It would be at the top of my list for a hybrid music/theater system in particular, where you need something powerful and bulletproof but still true to the source with music. (The review is super overdue but I will hopefully get it out in the next couple weeks.)
The 17B3 preamp is quite transparent - not as compelling musically as the amp, but accurate and dynamic.
Cheers,
TAWW