I'd guess that almost any speaker you carefully is going to be a huge improvement over the Polks. They're probably good for the money but compromises in floorstanders at that price point are huge.
I'd have a hard time saying no to these for 8k. They've got powered bass so should be fine powered by a big receiver.
Vandersteen Model 5A Floorstanding Speakers; Gloss Black Wrapped Pair - The Music Room (tmraudio.com)
These would be awesome, I'd be a little concerned trying to power them and a bunch of other speakers from a single receiver. You'd probably want to keep the volume moderate and eventually get a separate power amp to power them. You could get something like a Parasound A21 for $12-1500
Thiel CS3.7 3.7 Speakers RARE and COMPLETE | eBay
If you want to go new I'd be hesitant to spend 8k. It's such a huge jump from what you've got and you lose a ton of money if you decide you made a mistake. The Vandersteen 2Ces are a good place to start for around 3k. That basic model has been around for decades.
I'd have a hard time saying no to these for 8k. They've got powered bass so should be fine powered by a big receiver.
Vandersteen Model 5A Floorstanding Speakers; Gloss Black Wrapped Pair - The Music Room (tmraudio.com)
These would be awesome, I'd be a little concerned trying to power them and a bunch of other speakers from a single receiver. You'd probably want to keep the volume moderate and eventually get a separate power amp to power them. You could get something like a Parasound A21 for $12-1500
Thiel CS3.7 3.7 Speakers RARE and COMPLETE | eBay
If you want to go new I'd be hesitant to spend 8k. It's such a huge jump from what you've got and you lose a ton of money if you decide you made a mistake. The Vandersteen 2Ces are a good place to start for around 3k. That basic model has been around for decades.