You've 3 options
- convert the binary message into XML
- use an attachment to hold the message and have a placeholder XML document (such as <foo/>) for the content of the message
- convert some key pieces of information from the binary message into a small XML document that can be used for content based XPath routing while keeping the binary attachment around in case you need it
Any of those 3 options are fine. Clearly 1 provides the maximum amount of reuse of ServiceMix/JBI components like BPEL, XPath routing, XSLT transformation, XQuery support and so forth - whereas there is little the JBI services can do with binary messages other than just pass them along.
So the choice of 1, 2 or 3 depends on how much services you need & how much information you need to be accessible in the message