I think you can only bet or buy steam items with SS:

Steam Silver is a currency used on our site obtained from depositing steam items on our system. Steam Silver is represented in USD (1 SS = 1 USD). Steam Silver can be used to place bets as well as purchase items from the Stream Market Place. In the near future, there will an on-site exchange allowing users to directly list orders for Silver and Gold.

So in the future you can change them for gold what you can change for btc?