critique my setup -- weak link? best way to improve?

Re Seeker, nearly all preamplifiers ever made operate in Class A, and many/ most modern tube Preamplifiers can drive a 10K ohm load easily (which is to say their output Z is 1K ohm or less). I agree those are parameters that need to be checked out before you buy a tube preamp to drive an SS amplifier. You want input Z to be 10X or more higher than output Z.

There are some well proven bookshelf   style speakers that are affordable and you appreciate a much smoother sound after their broken in after 60 hours or so. Those speakers are the Wharfedale Lintons. They are usually on lower price around Xmas /black Friday specials.

Speakers would be the biggest bang for your buck improvement IF you can afford 1500-3k on new speakers.  I am personally a huge fan of Tekton Design Impact Monitors and Double Impact, but any of their designs with the seven tweeter array I'm sure is solid.  Expect to wait weeks though and have trouble getting through to them at times.  Although, they have some models available for sale right now on their specials section.

Otherwise KEF makes solid stuff if you don't like playing loud as I think their low end gets heavily distorted at higher volume typically at lower price points.

But yes, without knowing your budget, it's hard to give you advice.  Speakers are by far going to give you the biggest change in your system though.  But I'd say you'd have to spend $1500+ to get more than an incremental change.  I'd go as far to say that with some $2000+ speakers such as the tektons, it would absolutely change your system into a different animal.

Wish you the best of luck in your system journey!

Further to my earlier comment and to reinforce some of our colleagues like jrareform

here is a link to help prioritize and invest in the different components, if that can help. It also recommends to spend the bulk on speakers, then on the source, etc.

https://youtu.be/eNK9c6-rTrI?si=z-6DAHinMqvUqIDR

good luck and keep us posted on your choices.

At the price point of your system, you’d be hard pressed to upgrade without just getting a new system. But things to consider first, you have speakers that are ported on the back. Moving them would be a huge plus , but it sounds like that’s not possible. I’ve placed KG 1.5’s on stands about 20” off the wall and sound improvement was considerable. So here’s some suggestions, Crites crossover rebuild kit is relatively inexpensive. Add a Schiit phono stage and/or pre. A Bluenode ( latest version) would be a plus. Hold off on speaker cables , but definitely try better interconnects, Someting in the $100-200 range would be noticeable. Good luck and happy hunting, Mike B.