I didn't really test high/low pass filtering done in Allo Piano 2.1, as driver wasn't available (not sure it this is developed by now, but guys should be working on it) in DietPi. Other distributions proposed by Allo with Piano 2.1 driver are not functional solutions for Roon.
However, I already shared my test results on basic Allo Piano vs. Allo Piano 2.1.
The chips are different and Allo Piano 2.1 in even full range 2.0 mode it is much better sounding than basic Allo Piano.
So this this question: "Is it Piano 2.1 better (in pure stereo mode with one chip per channel)." - answer is YES