With what you have, I don't think you'll get much improvement unless you go to DAC's in the $1k-$1.5k used range. I had a DAC 1.1 and it is indeed very good and quite different than the 506.24 but it is not clearly better. For that you need to look to a Muse two ninety six, or an EVS Millenium II, or a Musical Fidelity A3 DAC, or other DACs in that range. Maybe even a Bel Canto Dac II (I have not heard it yet)
Good Luck
Good Luck