Here an excerpt I found on another site that I think best answers your question. I am also looking and hoping for another wireless option that will be more comfortable than sweaty headphones in the summer heat.
"The Nox700 and900 and Manticore use the Nordic nRF5340 chip utilized in both their ML85 and ML105 headphones. They are supposedly capable of supporting connections to Bluetooth 5.3 and earlier protocols, plus Bluetooth LE, but Nordic's datasheet specifically states, "proprietary protocols are also supported". Since no one (that I have heard of yet) has been able to establish a connection between the new Minelab machines and any standard Bluetooth earbud or headphone, it's apparent that Minelab has, at the minimum, chosen to make the headphones and machines Bluetooth LE compatible only. Currently, Bluetooth LE earbuds/headphones are not commonly available and tend to be expensive. But the real question is - did Minelab go a step further and apply "proprietary protocols" to the chip such that the machines only talk to Minelab's own Bluetooth LE headsets? We won't know for sure until Bluetooth LE devices become more readily available, and folks start trying to connect them. I'm not at all optimistic, since Minelab's manuals make no mention whatsoever about connecting other devices like they specifically did in the EQ600 and EQ800 manuals.

If Minelab went the completely proprietary route - that would be both disappointing and foolish. First, I just don't trust Minelab's ability to create/provide headphones with superior sound quality. The sound quality of the Minelab ML80 headphones that came with my Equinox 800 was subpar in my opinion, which was one major driving force for me to seek a 3rd party replacement. Second, Minelab would be overlooking an extremely important issue: everyone's ears and head interpret the sound quality and comfort factor of headphones differently - it's a monumentally personal choice. One person's favorite sounding headphone will be too "muddy", "bassy", or "tinny" to the next guy. Sound quality issues become even more personal when hearing loss in various frequency ranges is at play, as it often is for all of us as we age. Headphones that are perfectly comfortable for one person's head and ear size and shape are torturous and create hot spots in no time on another person's head. Those are the real reasons why offering only one proprietary wireless headphone option is an extraordinarily bad idea. And none of that even touches on simple comfort factors due to weather.

Hopefully we'll find that the Minelab machines are fully compatible with any Bluetooth LE headphone or earbud that eventually comes down the pipeline from 3rd parties in the future. In the meantime, my understanding is that the only option for going "wireless" outside of the provided ML85 or ML105 headsets is to utilize the Garrett Z-lynk or similar bluetooth transmitter/receiver set up and forking out the added expense and charging complications that go along with it."