"Air core" refers to a coil wound around nothing but air. So far as I know, the ART7, which I own and like very much, has an "amorphous core" Amorphous metal is an alloy with a non crystalline structure produced by ultra-rapid quenching (about 1 million ℃ per second) of molten alloy. The penalty for using an amorphous core or an air core coil is reduced efficiency compared to using a coil with the same number of turns of wire around an iron core. This is why the ART7 has much lower output than does the ART9. I don't know about these two new models that bear the "ART9" prefix, but it makes sense that the low output version of the new ART9 would be the one with an air core coil.
Phono Cartridge for $1,000.
Currently have Clearaudio Virtuoso MM cartridge . Wanting to go to MC. Found a Hana ML and a Sumiko Blackbird on sale for $1000. I am using a Musical Fidelity M6 phonostage so it will handle all. Is it worth it to change? If so, which one? I live in the sticks in Alabama so listening is almost impossible.