If I'm looking for "Tube Sound", why would I put a Tube Pre in front of a SS amp?


I'm purposefully not specifying speakers as I would like to know in general terms the arguments for and against. So, to the degree that speaker characteristics could also influence the choice, please  explain.  FWIW, I do not know a phase angle from an impedance curve so I will try and educate myself as we go along.  Hopefully, others may benefit too.
finsup
Has anyone in this thread addressed preamp-power amp electrical compatibility? This interface is also important, like the power-amp/speaker interface. Solid state amps tend to have lower input and output impedances than tubed units. Your preamp's output impedance should be at least 10 times lower than the input impedance it sees in the power amp. Other things being equal, this would favor a transistor preamp into a tube power amp, unless the tube preamp's designer has taken steps to lower the output impedance to where it will work with the lower input impedance of a solid state power amp. There are many exceptions. I have one ss power amp with a 100k input which is similar to a tube amp I have. Check your specifications, people. You need to have good electrical matches between all components before assessing sound quality or comparing "tube" vs. transistor sound. 
Atmasphere, I'm not so naïve to think that that type of behavior hasn't been considered before or even after, but as my Jewish friends might exclaim; "What hutzpah!". 
I have tried a CJ PV12 (preamp) with an older class D NAD amp, but eventually removed the CJ because it imparted too much hum. Now I use a Chord DAC to drive the amp directly and it sounds good, but not nearly as good as my all tube fully balanced Cary preamp and Atamasphere amps - and I'm driving a 4 ohm speaker with a 16 ohm amp with no problems because I’m also using ZEROboxes. Recently, I added an ISOCLEAN wall outlet and power cords and I’m in heaven! I hear so much more detail and the sound is even more natural. In fact, the signal is so clean I have no overly warm tube sound at all. Amps are plugged directly into the wall and other gear is running on a standard outlet with an ISOCLEAN power strip.
Tube pre with a SS power amp is a great way to drive power hungry speakers and get that great tube midrange and high end and a solid bass.  I have a cary slp 05 and classe ca2300 driving some Thiel 3.7s.  Nice wide and deep sound stage, very natural sounding.  Not edgy or fatiguing at all.  I would recommend this combo (tube pre ss power) to any one.  Just make sure you pay attention to the output impedance of the pre and the input of your power amp.  Need to get a good match.