C++ :: Variadic Templates And Overload Resolution

I'm trying to learn how to use variadic templates, and I decided a great example would be serializing a series of types into a stringstream:

Code:
// Send a fully constructed message.
virtual void send(ostringstream &msg) = 0;
// Construct a message from the arguments and send it.
// This is the usual entry point.
template <typename ...Args>
void send(Args ...args {

[Code] ....

This works fine, so far as I can tell. However, I decided to see if I could specialize the way certain types are serialized. I tried using a Google Protocol Buffer object as an example, and added this:

Code:
// Handle a protocol buffer type while constructing a message.
template <typename ...Args>
void send(ostringstream &msg,
const google::protobuf::MessageLite &protobuf, Args ...args) {
std::string msg_str = protobuf.SerializeAsString();
msg << msg_str;
send(msg,args...);
}

I would expect this overload to be preferred over the generic T overload when a protobuf object (which always inherits from MessageLite) is passed into send() anywhere in the list. However, this is not happening. I am getting an error message to the effect that << doesn't know how to deal with my concrete type, pointing at the T overload.