Maybe this will help:
CD128 vs. CD168 on paper
"One BB 1738 DAC chip vs. two BB 1792s. 24/96 vs. 24/192 upsampling. Sony KSS-213Q vs. Philips VAM 1202 top-loading transport. Balanced output stage vs. fully balanced circuit beginning at the converters. Fixed outputs vs. variable outputs. HDCD capability vs. none. Open/close button protocol to capture new TOC vs. auto read-in once cover is placed in transport well. 2.2V vs. 2.3V out. 102 vs. 110dB dynamic range. Permanent vs. optional illumination. 43 vs. 38-watt power consumption. Purely based on published specs, the differences between both machines seem quite minor but a look inside shows up further changes.... I could bore you with endless details but the upshot of the comparison was simply such a minor offset as to be far less than what tube rolling will shift in various directions. If your preamp has no remote control, the CD168's variable outputs hit that nail on the head. If you're a fan of black-out listening session, the CD168's halo-off feature will be preferable. If you fret over numbers -- one chip versus another -- buy the 168 and feel smugly superior. If money is tight, buy the 128 and know that those numbers mean nothing when the rubber meets the road in the kind of system context I image these players would find themselves in. In short, the CD168 is a feature-wise dolled up CD128 which sonically takes nothing away (not always a given). It thus justifiably shares the 128's prior Blue Moon award as a very slick, dialed machine and powerful recommendation in this sector. " - 6moons review
I believe the CD168 uses truly differentially balanced circuitry and that the CD128 does not. However, the question to ask is, does this really make a difference? There are well-regarded high end manufacturers who don't bother to provide balanced circuitry, because for home audio they don't believe the extra cost justifies the benefit. I have run a fully balanced system, and find I prefer my current single-ended setup. 6moons provides pretty comprehensive reviews of both the CD128 and CD168 along with some really nice pictures.