Next step up from Acoustic Zen Crescendo II's

What improvements are you looking for and what sound characteristics are most important to you?

I am a HUGE fan of Acoustic Zen.  Awesome speakers.  

I would second @soix question.  Also, how big is your room?  How far do you sit from the speakers?  What type of music do you listen too?  Aesthetcally, do you have any limitations or are you open to more interesting speakers?

There are a ton of great speakers in this price range. There are some that will definitely be an upgrade.  Just need to find the right one for your taste.  Obvious brands to start with are Raidho and Audiovector but there are many more like Vivid, Wilson Benesch, MBL (though your amps are low in power for MBLs) that are amazing and worth considering.  

@soix Looking for deeper bass and more punch in the mid-bass. This could be missing because I am on a concrete floor under carpet. So larger drivers would probably solve this.

@verdantaudio My room is 14x25 with 8' ceiling. I set about 8 feet from speakers. I listen to rock, folk, jazz, and vocals for the most part. I don't have any limitations aesthetically but do prefer a speaker that is not too "odd" looking if that makes sense.

I would need to go with a speaker that would be easy to unload without a huge loss if I didn't like them. The brands you mentioned are questionable on resale market. MBL's need more than 600 wpc?

Have you thought about adding a couple good subs or, even better, a Swarm?  That might give you everything you’re looking for and be much cheaper as well.  Just a thought. 

I looked up your amps and I thought they were 150w into 8ohm, 300w into 4ohms.  If they are are 600w into 4 ohms, they will work for MBLs.  Depending on the model, 300w into 4 ohms is minimum recommended power.  

That being said, the TAS review of the original Crescendos suggests that the claims of +/-3 to 20hz are generous and it sounds like you might be experiencing the same thing.  

So, if I am understanding this correctly you want the same imaging and immersive experience with tighter and deeper bass.  That is a tall task in that price range for a speaker without a subwoofer.  

I would look for a speaker that images well in the ~$30K range and add in two JL Audio f112 V2s.  Few options that could be interesting to you:

- Raidho C3.2 with a pair of F112v2s
- MBL Radialstrahler 116 with Fathoms
- Vivid Giya G4 with Fathoms

First off, why Fathoms?  The DSP for bass integration is going to be much better than you will get with other subs giving you a cleaner, more seamless integration.  They are also good to 19hz.  

Regarding speakers, these are going to deliver an experience that is different than the traditional Cone and Dome speaker in that they are going to immerse you in the listening experience rather than preset the sound to you.  That is what you should be experiencing with your AZs.  

MBL is going to deliver an extraordinary listening experience as it is completely immersive.  Nothing images like MBL.   The hybrid designs are much easier to drive than 101s and 300w is enough.  The cone portion of these is quite refined and should give you the tight punchy mid-bass you are looking for and the fathoms fill in the bottom.  They like an energetic room.  

Raidho is going to be similar to what you have in terms of imaging but with a couple exceptions.  The Raidho tweeter is generally deemed one of the best in the world and dispersion on it is at a different level.  That combined with the ceramic drivers will give you the tight, punchy mid-bass you are looking for and the fathoms deliver deep and powerful bass.  

Vivid Giya G4 is a smallish speaker with MASSIVE sound.  Technologically, these are at a bit of a different animal in that they are fiberglass cabinets with cone and dome drivers and are theoretically more traditional speakers but not completely more traditional speakers as the design is a "form follows function" approach the way the B&W Nautilus's were.  The design is intended to eliminate any standing waves, etc...  Truly one of the best engineered speakers in the world.  Immersiveness will take a step back in favor of improved clarity and highly refined mid-bass.  But aesthetically, they are different.  

The ideal speakers from Wilson-Benesch (Act One Evolution) and Audovector (R6) and going to put you over budget with subwoofers.  Though Wilson-Benesch would deliver that more traditional experience anyway which I am not sure will be as good for you.  

Full disclosure, I am a dealer for Vivid, Raidho and Wilson Benesch. I am talking to MBL and Audiovector but am not an official dealer of either.  I have no relationship with JL Audio.  

Based on your affinity for Acoustic Zen and the parameters you have laid out, I think these are outstanding options.