Do not get a better DAC. R26 is quite good with it's external clock input.
You need 10mhz Master Clock LHY OCK-2 with a good 50ohm Master clock cable (Messi & Paoloni, Times Microwave etc.) for that R26.
Use the R26 internal streamer as the master clock will clock the the streamed source as well.
That will align the planets. Trust me.
In terms of upsampling filters the R26 is better fed a pure NOS signal. If you had the A26, then I'd recommend using the upsampling filters as the delta sigma DACs take to those better in lowering the noise floor and creating overall smoothness.
Best of luck to you whatever you decide. New DACs are always fun.