I agree on those x14. Before I got the Kefs I was thinking possibly new x14s at $800 or 900 whatever they go for now but didn’t want to spend that much. Then the Kefs went on sale at 300. But the Dyns are better for sure IMO.
I also think those x14 are better than anything else around 500. But it’s all subjective. They would be for me. Ymmv.
Reason I’m so sure for me is when I got my D7 in main system I auditioned two dozen speakers over 6 months before settling on the D7. If my budget had been 5k (which it started at) I would have gone with Dyn Excite (whatever the 5k tower is, forget the number now, maybe x38 or x40). But once I heard D7 I knew I couldn’t keep budget at 5 k and would have to raise it a bit.
Dynaudio typically very hard to drive but that one x14 model isn’t as bad as most other Dyn bookshelf if you look at impedance and sensitivity and read the reviews.
then there are the x14a which are powered speakers but new they and x14 are outside of OP stated budget
Regarding SA1 that someone asked about, they have old tweeter instead of the new one that comes on D series. So they sound like classic Spendor which many love. For me it’s a bit too laid back. Some classic Spendor fans think the D series tweeter too forward but perfect for me. All subjective.
Incidentally the reason I ended up with so many Spendor and NHT bookshelves (I also have Superone 2.1 but never tried them for music, only HT) is they are some of only sealed bookshelves out there and three of my applications really work best with sealed speakers (one inside a cabinet, one on table near wall, third for rear HT surrounds mounted to wall).