I use onyx sand myself.
The best way I've found:
Rinse it 3 times, 1/2 a bag at a time in a 5 gallon bucket.
Add about 1/2 inch and add a handful of ground peat(eg Scott's brand etc) per sq ft, and about the same volume of vacuumed mulm from an established tank. Decant off the clear water and save the dirt(mulm/detritus) at the bottom. It's full of bacteria to instantly start up the tank. The peat will also help a good deal.
Then top this with 2-3 inches of sand.
I don't recommend using or mixing it with other gravels. Once that's done, you have a mish mash that cannot be undone and looks kind of tacky. After some time and replanting etc, all layered substrates get mixed together.
The peat and bacteria are for the initial start phase and there's not much added to begin with so that's not ann issue there.
So yes, oxyx is good stuff. It will move the KH around on you for awhile but if you do regular water change, are not trying to bred Apisto's etc, this is not an issue.
Regards,
Tom Barr