Sony str dg 510 and Toshiba A3 help please

When you say digital audio what do you mean (coax or optical)? What are you using for video connections to the receiver from the cable box and the A3? And what are you using for audio from the cable box to the receiver?

Unfortunately, the 510 (Unlike all of Sony's other receivers) does not have assignable inputs. Therefore, you can not connect your A3 up the way you have it ("Video 2/BD" and "SAT" are two separate inputs that can't be "assigned" to each other). Therefore you will have to run digital coax from the A3 into the "DVD In" of the Sony. Don't fret though, you can use any coax cable with RCA connectors on both ends (think composite video cables with the yellow connectors). It will work, you don't have to have fancy digital coax cables to make it work. If you are worried about quality, then you can always order a "digital coax" cable later. Just try it first.

Hope this helps,

I take it you mean you have the HDMI from the cable box to the Video 2 HDMI on the receiver and the optical audio from the cable box into the Video 2 optical on the reciever right? That means you have the HDMI from the A3 to the the DVD IN HDMI on the receiver which means you need to have the A3 hooked up to the DVD Coax in. I am unfamiliar with the A3 but if it only has an optical out and not a coax out then you may have to buy an optical to coax converter which can be found for around $25 I believe.