FWIW Id go for the apogee ADDA16x, I tried the big ben alone with my 192 and i didnt hear a huge diference to pull my wallet ( i know many GS say it makes a huge difference, I did not hear it), however when I installed the DA16x to my summing box mixing setup I heard a very evident-positve diference (my wife heard it too, if you are married youll know what I mean), so I went and bought the AD16x too.
Im guessing the apogee converters and the clock toguether makes both the difference, but also, the 192 are very good converters also, no one will tell you: Ohh Ugghh you are using digi 192 conversion, they are very good too. JMHO
Good luck