Cassette, chainring, chain compatibility
Will the Ultegra cassette work with the Praxis chainrings?


This is not quite the right question. The rings have to be compatible with a 10 speed chain that you'll be using on a 10 speed drivetrain. The Praxis web page for Buzz chainrings is unhelpful but other pages I found said that they are compatible with 11 and 10 speed systems.

Presumably you are putting these on a Dura Ace 7900 series or Specialized FACT 10 speed crank which will ensure the ring spacing is correct.

As long as the Ultegra chain is a 10 speed then it's compatible with the rest of the drivetrain. A Dura-Ace chain will be slightly better (and more expensive), as will a high end KMC or SRAM chain. Wear the Ultegra one out then make a decision about whether to upgrade.