Sound quality impact - preamp vs power amp?

The acceptable phrase is silk purse out of a sows ear. Either way its bollocks. A better preamp will be a better preamp and an improvement regardless. Speaker amp problems are speaker problems. Trying to solve the problem of a hard to drive speaker with an amp is a fool's errand. 

People asking about separates while pretending to care about cost always make me smile. If you really do care about the cost/performance ratio, in other words value, the answer is almost always an integrated. With integrateds like the Raven Reflection you have to go pretty far up the high end food chain to be looking at separates- and then you're talking $50k not the (relatively) measly $11k the integrated costs.

But the audio community has guys so spellbound buying ever more stuff, and separates do help you buy a lot more stuff. You can get mono-blocks, bi-amp, and lots and lots of power cords and interconnects. 

So a line stage preamp is the frosting and an amp is the cake, which can be layered in so many ways.  Both vitally important.  

op is a bit confusing, if everything else is high end then both pre and power should be of same pedigree. If funds are a limiting factor then get a better integrated amp that drives your speakers well. 
Consider speakers and power amp as one voice, so if your speakers are demanding (not only power hungry) you need the suitable poweramp, if not, then go for the better preamp.
G

Speaker amp problems are speaker problems. Trying to solve the problem of a hard to drive speaker with an amp is a fool’s errand.

That is nonsense and plain naive. There is more to sound than whether there are "problems" associated with easy or hard to drive. Perhaps MC has never experienced wonderful amp/speaker synergy before. It’s not all about the speaker being hard or easy to drive, it’s about how beautiful is the sound that can be created. Just because a speaker can be driven easily doesn’t mean it’s going to sound good or even the same with amps of similar specs. Why on earth would my speakers sound better with a relatively low powered SET amp than a SS amp with three times the power and with the ability to double down into loads of half the impedance?

I don’t think MC has ever heard the lucid and textured midrange produced by some 300B/speaker pairings while other single-ended triodes will produce more clarity and beauty, and yet others will be richer harmonically if not as incisively quick. All with similar specs and all being paired with an "easy to drive" speaker. MC apparently subscribes to the camp that if a speaker is designed to push more power of out amp, creating louder sounds, then it must be better and will work best in all applications. If volume is all you require from your speaker then your listening priorities are light years away from mine, not to mention grossly unrefined. Perhaps when I was 13 yrs old I would have agreed with you.