How to select and pair a preamp and power amp?

These two 
https://www.usaudiomart.com/details/649649181-primaluna-dalogue-premium-preamp/

https://www.audiogon.com/listings/lisa51jg-primaluna-dialogue-premium-hp-power-amp-tube

I would submit offers you can tolerate. Reliable,powerful and versatile.

I think most will probably recommend first choosing a power amp that best matches the speaker's characteristics and then pick a preamp that has the best synergy with the amplifier. The size of the room and the listening volumes also play into the decision, in my opinion. I've not heard your speakers but the specs, particularly the impedance characteristics, seem to suggest that they would benefit from a moderately high powered solid state amplifier to show their potential.  

At your budget I’d rather focus on quality and stick to integrated—neglecting need of extra ic pc etc. Maybe look to step up in quality from your current unit. Perhaps integrated from Accuphase, Luxman, Pass which I’ve heard (at friends/dealers) paired nice with Focals would work well. Goodluck.

if you use multiple sources i suggest finding the right preamp that suits your needs and built around it

The question boils down to this: what power amp at around 3K and what preamp at around 2K, in combination, are going to out-perform something like the Luxman 507uxII, which you can also get for under 5K?