Kenwood EQ

You don't even need an EQ actually--that's really only good if your head unit only had a single output.  You'll hook your sub amp up to your head unit's  set of non-fading preamp outputs, and later on when you get a 4-channel amp you'll use the two remaining pairs of preouts (front and rear) to send the signal to the 4-channel.

For now you can power the speakers by hooking them up to the head unit's purple (right rear), green (left rear), white (left front), and grey (right front) wires.  The solid color is the positive wire, and the striped wire is the negative one.  Also make sure you hook up the sub amp's turn on wire!