This is what you do. You take the DVI-HDMI out to the TV not the cable box….The cable box has only outputs for HDMI and Component, not an input.
You should now have two connections in the back of your TV, 1 HDMI from your macbook pro, and another connection from your cable box.
You will hit the menu button on the remote control for you TV and switch between the sources for whatever you want to view, whether it’s the Cable, or the Macbook Pro.
Do not go through the cable box, it will not work that way. If you want a sound cable, most Sony TV’s will offer two composite audio connections (red and white) for the HDMI you use for the Macbook Pro.
Treat the TV like a monitor. And then just switch between the sources depending on what you want to watch.
Oh, and once you have it plugged in, it will initially want to use the TV as an extended desktop, you can set it up for mirroring if that’s what you wanted to achieve. So initially if you bring your mouse to the edge of the display, it can cross over into the TV.
If you need anymore help, let me know. I sell Media Center computers (including macs), have set up several, and generally know pretty much any adapter you’d ever need to make it work.