Do you mean 2x AX64’s?
Or an AX64 and another interface that is TB3 but not a DAD branded product?
If so, which one?
Are you looking to get more than 256 channels of TB?
You could use aggregate IO on a Mac but it is buggy and annoying.
I’m using an AX64 and MTRX II linked via DADlink and they work great with essentially no extra latency from the slave unit.