Sony scd xa777es vs scd777es

Can anyone enlighten me as to the differences between these two units (other than their confusingly similar names)? Does either have balanced out? Which is considered to be the better unit? I see that one weighs almost twice as the other and is a top loader perhaps indicating better build quality. I am looking for a solid sony product as I have had good luck with my older es player.

Thanks to all
The XA has multi-channel capability while the scd is stereo only and if I can remember neither has balanced outs. I believe there is a different DAC architecture in the XA as well. The scd has better build quality in my opinion and was Sony's statement product along with the SCD-1. If you purchse the scd, and can afford it, have the superclock 3 and superclock power supply installed, it really improves the player on both redbook and SACD.

one correction to Chuck's post - the SCD-777ES *has* balanced analog outputs (my friend owns one & uses the balanced out to feed a MSB Platinum DAC). RCA analog output also exists.
I own the XA777ES with Superclock III mod. I beleive the SCD777ES is the better sounding one, marginally, and the XA777ES is harder to modify, so some modders won't do it.

The SCD-777es does not have balanced outputs(xlr) only rca's the SCD-1 has both which is a primary difference between the two machines.