I have never directly compared the 2, but I do have an XA777ES, and I would not categorically dismiss the quality of the CD playback without at least listening. In fact, the Stereophile review of the SCD-XA777ES actually concluded that it was probably worth it's price for CD palyback alone. The multi-channel "XA" is different from the 2 channel version in that when playing back CD it uses all 6 of it's DAC's, 3 per channel operating in parallel. My understanding is that this is quite different from the first generation Sony SACD players (SCD-1 and SCD-777ES). Additionaly, I have also had no problems playing any CD or CD-R on my Sony. In fact, it plays several discs that I have always had trouble playing on other players.
I bought my unit used here on the 'gon, and have been very pleased with all aspects of it's performance. Good Luck,