The slingbox solo is meant for only 1 piece of equipment to be connected to it. It incoporates a component video input conenction as well as svhs and composuite connections; however only 1 set of audio inputs. You must be connecting the blu-ray to the "output" connection by mistake if you still hear audio from your cable box.
You can however do a "cheat" or "workaround" by buying *@) rca y adapter cables (1 male to 2 female output configuration).
By plugging these adapters into the left and right audio inputs on the back of the solo, you then have 2 left and 2 right input connections. HOWEVER only one connected device can be on at the same time.
For example, if you are watching the blu-ray, you need to turn off the cable box; otherwise the audio will overlap and cause issues and potetial hardware failure.
The "REAL" solution is to change out your slolo for an HD PRO which alls the conenction of multiple devices and has seperate audio inputs for each; not to mention picking up HD picture quality thoughout your own network and remotely (as long as your upload speed can support those resolutions).
Look closely at the back picture of your solo here and you'll see there is only 1 set of audio inputs; NOT 2: