Sound quality impact - preamp vs power amp?

As usual, some are answering questions that were not asked, and some are making assumptions.  However, the question as asked may be too open ended to properly address without more detail.

It sounds like the OP is saying that the system is already of good caliber all around.  In that case, a better pre or amp would really offer limited improvements, generally speaking.  If one of those were long in the tooth, or lacked a feature or connection option one wanted, that might tip the scale, as it were.

 I am in agreement with @tvad.  I would like to point out that it’s easier to get a flat impedance curve with lower impedance speakers, and  that due to that lower impedance those speakers will most likely (speakers like tvad’s Soundlabs excepted) be less sensitive.

The amplifier is far more important than the preamp even if it has a phono stage. Amplifiers and how they are matched to the loudspeakers can make or break a system. See what happens when you put an 8 watt SET amp with Wilson's. Some speakers require a lot of power. Without it they are lifeless. Makes no difference what preamp you are using. 

Sounds like a hypothetical question to induce responses. If the OP was serious, he'd simply consider an integrated amplifier within his remaining budget. Would you put an entry-level cartridge on a high-end turntable? Which is more important when all things are important? 

Speaker and amp tech may not change so often as the preamp/streamer/DAC   So my view is nail those down first.  Make sure you can return whatever you get. Happy hunting.