what impacts the sound quality more amp or pre-amp

Everyone is correct and its obvious they have all had vast experience in this hobby. If I were you I would upgrade my preamp first, you might look at some used CJ like PV10 in particular.

You get a real bang for your buck and you get very tubey sound but totally grain free and non-fatiguing. Just an option.

Dvdgreco, if your looking for advise on the best bang for your buck system improvement, why not post your system? Be careful of advise touting personal technology preferences without considering your personal budget and system.

my system is

B&K ST202 (I think its a sonata series??)
B&K 10ProMC
Alon II speakers
Jolida 100 cd

Are you sure that you want to rule out an integrated?
Personaly, I don't consider separates unless I am prepared to spend thousands, at least couple of them.

The Alon II speakers are specified as 87 db efficient and are, I think, 4 ohm nominal impedance. This is a difficult load for most tube amplifiers to drive.

My personal feeling is that if you want tube sound that you should go with a tube amplifier. I think this makes the most difference. But it implies certain speaker choices too.

From a practical point of view, it is going to be challenging to find a tube amplifier for $500 - $800 which will be able to reasonably drive your speakers.

In the context of your system and with your budget, my feeling is that a tube preamp would be your best bet.

The Mapletree Audio Line 2A SE preamp is $760 new. It will likely survive many system changes and upgrades that may or may not be in your future.