I have never seen a diamond disc, but sure will look after this thread. I have seen shellac records break when dropping on a
period-correct changer that was made to play them, please be careful.
My go-to setup for playing 78s is any Zenith, Magnavox, VM, RCA, Garrard, BSR or similar vintage record changer with a flip-over stylus.
Most of the 3 mil are sapphire for 78s. MG and LP are the same, most have a "78" side, confirm but don't assume.
45 rpm records are best on a player designed just for them, using the adapter on a record changer is less preferred.
Cartridges are another subject but assume any player can be fitted with a new/old stock cart and the stylus can be selected.
If the cartridge is OK, a stylus is probably available no matter how old it is. Cartridge compliances shrink/harden with age even NOS carts, sounding dull and this is why there is a surplus of stylii to fit them.
There is a weekly record collector swap meet in my area, I saw folks walking around with portable players to "sample" discs.
I heard no music (hard rule?) saw nobody selling players, so I never went back. Not my bag, just play and enjoy!