Actual information on Claravox

FWIW, I am happy with my Adam t5v. Just one speaker does the job nicely. Don’t know how much they retail for in Australia, but it cost about £120 about a year ago. 

Thanks, I am assuming I should look with something with a large-ish speaker (10"+), or perhaps a couple to help with the dynamic range. Vendor information is confusing. I have heard guitar amps are not the best because the signal coming out of the theremin is too hot for them

Keyboard and bass amps work.  I use a 15” bass amp and a 12” keyboard amp together. Or any guitar amp after a pedal that can control output.

Some guitar amps that have plenty of clean headroom and/or high and low sensitivity inputs can be suited for theremins, but many will be overdriven by the hot signal. I usually put a Behringer preamp (Tube Ultragain MIC100 or MIC200) right after my theremin to adjust the outgoing volume to effect pedals or amplifier and also used it to mute the signal of my Etherwave Plus instead of draping the audio cable over the volume loop. Not so much an issue with theremins that have a mute switch.
I've done gigs and jams with a Vox Pathfinder 15EHR, now have a H&K Era 1 Acoustic amp, at home I have the Era 1 paired with a modified Fender Pawn Shop Special Greta, a 2W or so small tube amp, with a vintage '50s radio extention loudspeaker cabinet that matches the Greta wonderfully, very efficient loudspeaker with a beautiful sound character.
The new VOX keyboard amp may also be interesting, it's quite small and light and not terribly expensive.

Vox tonelab is a good option to control level and offers a tube in the signal path.  Lots of options to play with but I usually play clean and use it to run two amps.  I also heard use the active Input in amp if available.  I love my Claravox.  It is quirky but worth it.  I love this whistle sound I developed with the editor.

I sniffed some of the MIDI traffic going in and out of the Claravox app, and found these NRPNs:

NRPN 1025: Set MIDI Resolution (0 = 7 bit, 8192 = 14 bit)
NRPN 1026: Set MIDI Channel In (0 = omni, ...)
NRPN 1027: Set MIDI Channel Out (1-16)

There's a bit more undocumented stuff going on. For example, Moog's MIDI manual does not explain how to configure CV mods, which is essential if you want to fully control the instrument without relying on their official app.

So I asked Moog support. No dice. They will not share any information on undocumented MIDI messages. That's quite disappointing, because this means users have no alternative to their proprietary app. If this really is supposed to be an instrument for a lifetime, I sure hope Moog intends to maintain the software for decades. Will it still work on modern Macs and Windows in 2050?

Other NRPNs sent by the app during initialization:
NRPN 1011: Unknown
NRPN 1012: Unknown
NRPN 2383: Unknown
NRPN 2384: Unknown

These are probably not important though. They're only sent to the instrument once when it's connected to the app, and always with the same static values.

The only important undocumented messages (apart from the discovered NRPN 1025-1027) are related to the CV mod configuration. I will try to figure it out.