The adapter board you are working with is not a product of Digi's. Only the XBee module is. So I can't say if you need extra hardware or not with that board. But generally speaking, jumbled text means one of a few things. First, a baud rate mismatch is occurring. That simply means that the Serial data rate your device is running at is at a different rate than the XBee modules are. To resolve that, simply adjust the baud rate on the XBee to match the devices baud rates.
One of the modules (receiving module) is in API mode and you are actually getting Hex API data.
A voltage mix-match is occurring on either the Tx or Rx side. That is the XBee is a 3V device and your processor is a 5V device and there is some issue with the level conversion circuit between them.