Bookshelf speakers for $500ish

One of my favorite "bookshelf" speakers over the
years was the Sequerra Pyramid MET-7. They do't go very deep,
but their mid-range and treble are excellent. I used a small
subwoofer with the pair I owned, but without a X-over it's
hard to get a good blend. The speaker has been in production
for 30+ years, and while a new pair is well above your budget,
used examples can be an excellent buy (I recently saw a used
pair for $600), and there is a pair currently for sale on Ebay
for $375.
Check out the Internet for various reviews.

Here's an interesting listing for a pair of Rega RS-1s. No affiliation with seller.

Check out the Vanatoo Transparent Ones if you don't mind buying active. Tons of rave reviews! They start at $499.00 in black with multiple options including Bluetooth and Airplay.

From the Vanatoo website:
"Check out our home stereo speakers in the comfort of your own home with the Vanatoo 30 day audition period. If you decide within 30 days of receiving your Vanatoo speakers that you are not totally satisfied, you can return them for a complete refund. All we ask is that you pay for the return shipping".

Michael Fremer bought the review sample :-)

I think you're going to have problems replacing the Dynacos. One thing that's nice about the A-25s is that it delivers very tuneful and deep bass for its smallish enclosure size. The highs are rolled off and the midrange is not as articulate as more recent loudspeakers, but the bass makes it sound close to being a full range loudspeaker. I suspect this quality is very appealing to you when listening to small combo jazz. I can't think of a loudspeaker that is smaller than the A-25s that have anywhere near its tonal balance.

i've had the DYNACOS and had/have the REGA R1s (now the RS1s) in a prior B system/current surrounds in my HT kit

The REGA bookshelves smoked the DYNACOs .... full stop IMO.

http://www.stereotimes.com/speak121305.shtml

The Rega R1 Loudspeaker - A New Budget Reference
December 2005

"....Immediate impressions are a clear and transparent portrayal with very high detail retrieval, fast and controlled transient response, and superb musical timing, both in articulating rhythms and tempi, and in placing instruments within the temporal flow and context of the performance. The RR125 is an outstanding mid/bass driver, sonically and musically right in line with the midrange performance of Rega’s amplifiers and phono cartridges. Get the midrange right and everything else will fall into place. Get it wrong, and all the king’s horses…

The Rega R1 becomes my new budget reference speaker. In addition of its ability to get the fundamentals of music right, it adds clarity and resolution, and an ability to lay out a vivid and coherent 3-dimensional stereo image. In small room applications, what more could you want?..."