Sound quality impact - preamp vs power amp?

Equal. However, most modern amps have enough gain that they can be driven by the source components (assuming decently sensitive speakers), so a good amp only needs a passive preamp with quality input switching and volume control. So start with a good amp.

Yes, everything gets connected to the preamp but all signals eventually make their way to the speakers. The speakers are the heart of the system and have the greatest influence, especially if they’re decently efficient. 

I believe the whole point is to optimize the synergy among your components & room to best connect you to the music and stir your soul.

Bingo!

A synergistic system that stirs the emotions is the ultimate goal. This can and often does result from very unusual combinations. You cannot simply throw money at the problem either. So when I see someone is using $1K speakers with $10K amplification, and vice versa, I no longer assume he/she is a noob.