Linking tXMLMap output directly to tRESTResponse will do the auto conversion of XML to JSON, assuming the current response Content-Type is application/json.
The problem we have so far with this auto-conversion is that we can control some aspects of JSON serialization. For example, we can not have JSON produced as "". But we can configure it to drop the root elements which may produce the expected output, there's a drop root element JSON property is available
Can you please experiment with tXMLMap ?