What should I upgrade or add

I have this Sony MHC-LX10000 and it has really good bass but I think a sub is missing but what should I also upgrade the stareo or the speaker and what can I add to make my experience better and more nice.

I have this Sony MHC-LX10000 and it has really good bass but I think a sub is missing but what should I also upgrade the stareo or the speaker and what can I add to make my experience better and more nice.