Devialet 440 Pro CI not sounding great...

[ogs]

I am not surprised you like the R2R DAC. One of the best (if not THE best) design here is totaldac. Available with both tube and solid state output stages. Very expensive due to extremely expensive resistors in the ladder chain. A Devialet with a DAC like this built-in is probably impossible due to place constraints, but it would most certainly sound good.
I think it is important to remember that the DAC Devialet is using works in a very optimised environment and probably sounds better here than in other designs using the same chip.
You may get some of the character of the Aqua La Scala through the ADC of the Devialet, but not all. Good luck in choosing!