I think to make this discussion simple, we have to talk about amps first. There is a line of thinking that tube amps deliver a certain midrange bloom, openness, airiness, upper midrange smoothness, relaxation, that is difficult to duplicate with solid state design. On the other hand, tube circuits have difficulty delivering the overall dynamics, the bass weight and extension, and especiallly the woofer control, the ability to stop and start the bass driver in an instant, that solid state can.
To be sure, there are some very fine solid state amps available that have overcome the typical solid state drawbacks of upper midrange coolness and hardness and a mechanical sound that good tube amps lack. On the other hand, there are a handful of tube units which have very excellent extension at both ends of the frequency extremes and don't sound rolled off in the high frequencies or the lows. However, if you want the ultimate in woofer control, in my opinion, that can only come from a solid state amp.
One way which is deemed to give the best of the solid state and tube worlds is to use a tube preamp with a solid state amp. You can get the speed and dynamics and the bass weight and control of solid state while retaining the midrange bloom, airiness and lack of mechanical sound with tubes in the preamp. This can work very, very well and go a long way to solve the problems that each type of circuit supposedly has. But remember that today there are solid state amps and preamps that do not have that typical solid state sound and there are tube amps that have excellent bass weight and sufficient dynamics to not bear most of the typical drawbacks of tubes. On the other hand, although I have heard a handful of tube amps that have great power, dynamics and extension in the lows, in my opinion, there are certain characteristics that solid state amps can have that tubes will probably never be able to duplicate. As good as a handful of tube amps sound, they do not sound like solid state in these characteristics. Those that will tell you different have dismissed these characteristics as not being important and are not listening for them, which is their right to do, as we all have our own listening biases.
I would forget about tube vs. solid state debate. A great deal of the work in getting a good system is knowing which units work well with which (matching). At the highest level of execution today, this debate is nearly passe.
