Fro,
In my experience, TriPlanar VII and Schroeder Reference (my preference being for the former).
Also Graham Phantom, by reports of several owners who've compared with one or both of the above arms and found it at least their equal for a top ZYX (and other carts).
I expect there are others...
The DP-6 is brilliant at its price point, but the Atmos and UNIverse were not designed for price points. Each was the ultimate expression of Nakatsuka-san's ideas and craft at the time he designed it. The UNIverse in particular repays every improvement in a system by providing more of the music. Shortchanging it by using a second tier arm just wouldn't make sense (just my opinion of course). FWIW, I know two UNIverse/DP-6 owners who upgraded to TriPlanar and were stunned by the improvement.