If you're getting that error then you don't really have XML, you've got something masquerading as XML and the usual tools aren't going to handle it (well-formed-ness is sort of a bare minimum "You must be this tall to ride" requirement for data to be XML). The normal way to embed data that might contain characters that would be mistaken for markup is to either embed it in <![CDATA[...]]> (presuming your data doesn't contain any embedded ]]>'s of course :), or to encode it using something like base64 so that there's nothing but vanilla characters (but then it's incumbent upon the receiver to reconstitute the original data).

Unfortunately both of those options are going to require you to get whatever's emitting the nauga-XML to fix their output (then again it's their problem for creating output that's not well formed to begin with . . .).

Update: And if you read the XML spec not being well-formed is a fatal error, and processors conforming to the spec are supposed to toss up their hands and halt normal processing.