I wouldn't be too surprised to find out that Sony is using better DA converters than Bel Canto -- As Plato says, separates can be an improvement over integrated units, but that's because they frequently reflect better design and the use of higher quality parts. Based on my own limited, and unsatisfactory, experience with a Bel Canto amplifier -- which left me wondering about their design and production values for their entire product line -- I wouldn't be too surprised to find out that Sony's XA5400es has a better DAC built in than Bel Canto is offering separately. Sony, after all, has produced some of the best CD and SACD players ever made.
I have to say, personally, that while I have found separate preamps and power amps an improvement over most integrated amps, I have always been skeptical of the "separate transport and DAC" as an improvement over a top-quality integrated CD player like your Sony, but I recognize that YMMV.
I have to say, personally, that while I have found separate preamps and power amps an improvement over most integrated amps, I have always been skeptical of the "separate transport and DAC" as an improvement over a top-quality integrated CD player like your Sony, but I recognize that YMMV.