In my view, speakers selection comes first - if you're into SS amps. Audition speakers of diverse topologies, technologies and brands until you find the sound signature that pleases you most. If you enjoy tube amps, your speaker options will be somewhat constrained to speakers that play well with tube amps.
SS power amp selection comes second, but the choice here is more binary as it revolves largely about gain, speed and maximum current delivery - headroom. Looking at an amp's power transformers' VA rating, power supply architecture and filtering capacitance will often be a pretty good indicator of a power amp's speaker-driving capabilities and determine whether it's a good candidate for an audition - if the chosen speakers are the slightest bit hard to drive, there is no point listening to inadequately sized power amps. As the saying goes, there's no replacement for displacement.
A power amp should not be used as a tone control; it should amplify the preamp's input signal. This is not to say that power amps don't have sound signatures, but the main point is to ensure that said sound signature is synergistic with the chosen speakers'. It may sound like I'm minimizing the power amps' importance in a system, but I definitely am not. The wrong power amps can ruin your whole day (and possibly your speakers).
A preamp, in my opinion, contributes more to a system's end sound than power amps - as it should. The preamp is where the speakers' sound signature is further refined until the desired end sound is attained.
I am in the camp that believes a high-end pre is crucial tò successful system building, and that going preamp-less in a high-fidelity two-channel system (ie relying on a DAC's volume control) is nonsense.
Speakers, amps and preamp constitute the core system. Sources come next, and unless a single source is planned to be used at all times, there is no point in starting building a system from the source.
