Upgrade

That budget would get you a set of Synergistic Research Element CTS speaker cables that will do exactly what you want - larger sound stage, more liquid and open- and with much greater dynamic punch. You could probably afford to have Michael Spallone upgrade their power supplies for truly jaw dropping performance. The main downside being when you hear just how much difference quality cables can make you will be spending a lot more money on them in the future.  

https://systems.audiogon.com/systems/8367 (These have the Michael Spallone power supply mods) 

Or you could add a full room treatment of Synergistic HFT, both room and speaker kits, not as staggeringly huge as the CTS cables but close. 

But if it really is a deep wide dynamic liquid sound stage you are going for then ditch the ML and get a Raven integrated. You could probably sell the ML and AR for enough to get within $3k of a Raven Reflection MkII integrated, which will be an even more staggering improvement than any of the above ideas. Which is really saying something. https://www.ravenaudio.com/product/reflection-mk2/ 

Those seem like really nice speakers but they bottom out at 40. [from website: 40Hz to 16kHz, ±3dB]

I have some speakers now that go down to 38 hz but the presence of just one REL sub does quite a lot, very noticeable, for the entire spectrum. I got that $1900 sub used for $900 and I am pretty convinced that a second sub is necessary. (Just waiting for a bit to see how some other things develop.)

Perhaps get a sub or two as a tryout and see what happens?

Try LOMC cartridge. Or MI. 

I agree with the other folks here who mentioned a sub.  I would look at adding a very refined, sealed sub.  JL or REL make outstanding subs.  

This will help deliver a bigger sound stage on a lot of tracks as you will improve accuracy and frequency response below 50hz.  

The other option would be to look at a nicer cartridge.  Especially with that JC3+, something like an Ortofon Cadenza Bronze could be interesting as it will add a bit of sweetness to the overall sound profile.  I run a tube phono stage and have all tube gear so I run the more detail oriented Cadenza Blue as the Bronze would just be too much.  

I am an Ortofon dealer. PM me if you are interested.