You have options here, but if you want to use a Z wave Leviton master, you have to use the auxiliary that goes with it which will also be a Z wave Leviton device.
There are some other brands where the auxiliary does not have to be a Z wave device but you still have to buy the specific auxiliary that goes with that specific master dimmer.
The reason is that there are several different ways for an auxiliary to communicate with a master and you have to get ones which are specifically matched.
There’s no situation where you can keep the existing auxiliary, though.