Why Tube Pre-SS amp over SS Pre- Tube amp?

Another factor in that paradigm is that tubes in a pre generally last 1000s of hours, while in many power amps, their lifetime is more limited. For that reason, cost of NOS power tubes is much higher. So total operating cost can be higher for a tube power amp than a tube pre.

For me it was experimenting w/gear back in the 80's when I came across the big SS amp/tube pre combo & it always was a good matchup. Over the yrs. I've discovered that a well implemented design, be it SS or tube, will give you the sound you desire.

I agree w/Jond "don't get weighed down by dogma" and will also add my mantra of "trust your ears".

Having owned both SS and tubed amps, and SS and tubed preamps, I believe the largest change in sound comes from the amplifier. If one wants the sonic signature of tubes, i.e. extended grain-free highs, holographic image and magical midrange, I'd suggest starting with a tube amp and a SS preamp. I have never heard a SS or chip/digital amp that has the three dimensionality of a tube amp. My recommendation runs counter to commonly offered advice, but it's how I'd start over if I was building a system from scratch.

BTW, one CAN have excellent, deep, controlled bass with tube amplifiers with careful amplifier selection and proper matching with loudspeakers.

If you want to know the technical rationale for choosing a tubed preamp and SS power amp, tubes operate at hundreds of volts and are much more efficient at voltage gain. Solid-state devices like transistors operate at lower voltages, like tens of volts, but due to their lower output impedances, are much better at driving current, which is what your loudspeakers need for bass control and high volumes. Since most voltage gain is found in preamp and power amp input and driver gain stages, tubes are a better bet for these applications, whereas for power amp output stages, SS devices are superior. This doesn't always translate into sonics that we like, note SET amps that have very high output impedances but many like the sonics of these amps. Like you noted, in most applications it is better to use a tube preamp and SS power amp, especially with loudspeakers that present difficult loads to the power amp.

I agree with Tvad. Much depends on the specific character of the components you're considering. Of all the combos I've tried, I'm happiest with my SS preamp driving a PX-25 tube amp. While the tube/SS pairing is touted as being more likely to be successful, nothing beats figuring out what your sonic preferences are and evaluating specific combinations from that point of view. Following a "generally applicable" approach isn't helpful if the particular combination you're evaluating doesn't float your boat.