It seems that you want to know if the Slingbox needs the IR Blasters in order to work with a Comcast DC50X Digital Transport Adapter. Once you connect a TV source (any box provided by your cable service provider), you will always need to use the IR Blasters.
Keep in mind that this accessory is the one that allows you control the TV source when connected to your Slingbox. So, it is mandatory for you to use the IR Blasters whenever you use a set top box. If you need to purchase the IR Blasters, check this link.