am not sure if a tube preamp would work well with the Yamaha NS 5000 speaker. I am also not sure if I would get the benefit of super low noise floor of the Benchmark AHB2 with a tube preamp.@yyzsantabarbara A good tube preamp had better not be a tone control! It should just be neutral. This is not a bandwidth thing either- for example the line stage our our preamps goes out to about 400KHz- higher than many solid state preamps. The thing here to be aware of is the brightness of solid state is not on account of frequency response; just about all preamps tube or solid state will be nice and flat in the audio band. The brightness of solid state is the result of distortion, and really not a lot of it because of how the ear works.
The ear uses higher ordered harmonics to sort out how loud a sound is and because it has a range of over 120dB, it has to be very sensitive to higher ordered harmonics. So if a circuit makes higher ordered harmonics even in very small amounts it gets interpreted by the ear/brain system as brightness and harshness. We are talking about THD that might only be 0.005%.
That is different from simply being neutral. Your Yamaha speakers might be easy going on top, but if you put something extended that is also neutral this will not cause them to sound rolled off!
Regarding noise, its nearly all power amps are lower noise than a preamp. Yet people use tube preamps in systems with **horns** all the time; your Yamahas are not as efficient as horns so you've got no worries in this department :)