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

Agree with Eric's explanation, electrical compatibility between the amplifier and speaker IS most important as is the output impedance of the preamp being ideally suited to the amplifier. Beyond those two very important parameters much of the rest regarding some of the other comments is subjective. I would further comment that generally tubes are more ideal for use with a speaker having a higher and more stable impedance however there are tube amplifiers with quite low output impedances that can work with speakers with more difficult loads.

Tube sound these days varies quite a bit but in my experience I generally hear the effects of tubes to a greater extent when using a tube amplifier. Using a tube preamplifier with a quality SS amplifier, well the character of the SS electronics always reveals, to me at least, that I am listening to SS. Nothing wrong with that as each have their particular virtues and that is why no one can specifically answer your question but you when listening to a specific setup.

"However, if you really want to treat yourself go with tubes all the way. That way you get the additional benefit of reduced higher ordered harmonic distortion, which to the ear sounds like brighter and harsher, and is the thing with which transistor amplifier designers struggle. "

I would generally agree with the comment above. To me the really big difference AND big deal with tubes vs SS is the harmonic resolution AND that undefinable attribute of "presence" that the BEST tube designs really deliver that I rarely hear consistently with SS. I try to be fair minded, objective and balanced in these discussions but I REALLY agree with Atmasphere's comments. I have a good audio buddy, all tubes over the almost 20 years I've known him that has gone over to the "dark side":), tube preamp, ss amp, i mean superb SS. While I really like the presentation and at times it makes me question things, over time I notice that it just does NOT have the emotional connection to the music as good as it is. To each his own and remember this one simple point, it's all an illusion anyway, whatever floats your boat is most important, just listen and enjoy!

Very nicely stated and great advice cdk84.