Emm Labs XSD1, Eximus, Mytek, Naim, Moon 750/650, AMR-77, Wadia 861SE with GNSC mods, Meridian 800 are some of the digital front ends I have heard extensively. Emm Labs was probably the most musical, but had the advantage of full AIR Tight amplification, ATC2/ATM3 monos. Eximus I think is pretty good value/performance.
Main point is you will probably get more resolution out of a 24/192 DAC than the 32bits SABRE based units.
The best digital I've heard extensively is a non red book standard custom built DAC that dispenses with the clock info from the transport and uses clock info extracted from the data itself, ( the only commercial DAC I'm aware of that does this is the Orpheus Heretage ), proprietory A/D & D/A algorithms that eliminate sine x/x errors inherent in all red book material and a few other bits.