I am interested in this model also, while trying to compare it to the STR-DH720 as well.
I did a comparison on the Sony site
and can only determine that:
1. STR-DH720 had DCAC features while the 520 did not
2. STR-DH720 had NO night mode while 520 DID have
3. STR-DH720 had no 3D pass-through while 520 DID have. (Probably incorrect as it is listed on the features page for both Sony models.)
Sub for both models must be self-powered. The STR-DH720 has two connectors for the sub and the 520 has one.
Looks like the STR=DH720 has better speaker connectors on all speakers, while the 520 uses spring type connectors for surrounds. Further, the 720 has more analog inputs and a bit more power output (140W vs 130W total).