To "wax poetic" means to become increasingly verbose and romantic in speech. To become more and more like a poem.
"Wax" = increase, "wane" = decrease.
It has nothing to do with vinyl records and bullshit hip-hop, "yo."
"Not to wax-poetic, but your eyes glimmer like the ocean on a summer evening..."
To speak in a very eccletic and influential manner. The term probably comes from the usage of the term wax, which is another name for vinyl records meaning that it is recorded and musical, and poetic, which obviously refers to the stylized nature of the speech.
Yo I don't want to wax-poetic on y'all about the nature of hip-hop 'cause you's minds are too ignant to comprehend the complex theories I be spittin. Ya heard?