The obvious differences of a C-300 vs A-300:
C-300-Full BDA Lisence for Full Bluray menu(BD-Live & BD-Java)
A-300- Full navigation menu(no BD-Live, no BD-Java, no official Bluray menu support)
C-300-Can add Blu-ray Drive to play commercial Bluray discs.
but C-300 cost more than A-300.
The C-300's Full Bluray menu support compatibility of ISO or Bluray Discs is no way better than a full standalone Bluray player like an Oppo.
A-300-not as many USB ports as C-300, but for h/w ports and such, just look at Syabas compatibility chart on thier website.
With the above main concerns for me and looking at the comparison chart, I sold my C-200 for an A-300.