What do you hope to improve about the ZS10 Pro? Some of the recent Dunu offerings seem to be getting a lot of praise. I had the Zen for a while and it was a very fun, dynamic IEM. I’ve been starting to see open box or second hand units around your budget. They are a sensitive IEM so you might have to pick up an IEMatch with some sources to lower the noise floor. The EST112 and the SA6 might be worth looking at depending on what type of sound signature you are looking for. They are 3 different flavors.
I’ve also heard good things about the Final A3000 which doesn’t get talked about as much. There are a bunch of options honestly. If we know what your sound and music preferences are we might be able to direct a little more specifically.
I have not tried the SA6 but my guess is if you are hungry for bass they might not satisfy your appetite. They are an all BA configuration which means you won’t get the same big, impactful bass as you would with a dynamic driver or a hybrid. It would be nice and tight and textured though.
The Dunu Zen has very satisfying bass, very impactful and lots of detail and texture. Some of the best I’ve heard in IEM or headphones. I haven’t heard them but you could look at the iBasso it03, Sony XBA N3, and Campfire Polaris V2. I have owned the JVC HA-FDX1 and it had some nice bass as well, but a bit more neutral tuning overall. Very nice, well built IEM but the fit can be a problem for some.
You might also consider picking up one of the iFi portable amps that include their XBass feature. It really works and it is a lot of fun with the right pairing.