Connect Two Block Rockers With Wires

How to setup a two block rockers using a headphone splitter and cables.

There are links to the stuff on amazon:

Block Rocker- big battery powered speaker with inputs

25-Feet Gold Plated 3.5mm Male to 3.5mm Male Stereo Audio Cable

Belkin Y Adapter; Mini Stereo Plug, Headphone Splitter

Why?  
This was a blog post I wrote responding to a question on amazon.
 

You could also do this with an RCA jack (like from DVD player), by adding an RCA to headphone adapter.