I think you only need one queue per actor? And then one worker per CPU core? I believe that how Erlang does it, and do millions of actors without any issues...
Sending a message between Actors can be just moving a pointer to a piece of shared memory.
I think sending messages is more about the way you think about concurrency, more than the implementation.
I have always found the "one thread doing "while True receive message, handle message" much easier to reason about than "remember to lock this chunk of data in case more than one thread should access it"