Thanks for posting to our Forums! I'm sorry to hear that the Slingbox is playing an echoing audio under HQ using component cables with analog audio cables.
For this issue I would try to remove and install the application again on the phone. You will not have to pay for the application again as long as you are using the same iTunes account.
Also to change to the SPDIF audio input on the Slingbox PRO-HD, You will need to run only the component(Red, Blue and Green)cables, and the orange SPDIF cable from the cable box to the Slingbox. Then all you have to do is a complete factory reset to the Slingbox and run through the setup on Setup.Slingbox.com.
Below are some articles that will assist you in the trouble shooting:
Hope this helps!
The Sling Media Moderation Team