Service-based modalities are becoming more prevalent in metacomputing and grid computing. The absence of pre-existing client-server relationships imply the use of standardized, self-describing protocols which typically suffer from performance deficiencies. The RMIX framework is designed to permit heterogeneous entities to interact via a service-based paradigm while enabling protocol selection and dynamic protocol switching. In particular, an RPC-compliant communication provider enables multi-language heterogeneous clients to communicate with servers and leverage well-established RPC/XDR mechanisms to support interoperability without sacrificing performance. This paper describes the RMIX-RPCX communication substrate, and presents preliminary results that suggest its potential value in enhancing service-oriented heterogeneous meta-computing.