I understand that you want to know how to change the codecs that will allow you to run the WMV and WMA video and audio.
The main issue is that you have two different Slingbox models. You have the Slingbox PRO (the first one) and the Slingbox PRO-HD (second one). While the Slingbox PRO runs the WMV and WMA video and audio codecs, the Slingbox PRO-HD runs a different type of codecs: H.264 for video and AAC for audio.
Unfortunately, it is not possible to make this adjustment since they are totally different products. We do apologize for the inconvenience this might represent for you.