resistors - How to find the equivalent resistance for YY parallel connection

I am trying to find how to break apart a Y-Y connection to find the equivalent resistance. I understand how to find the equivalent resistance for 2 Y circuits in series, but not parallel. I understand how to transform from delta to Y and back, but am unable to find a simplified circuit for this design:

o--------o--------------------o
|         \        o        /

|          \      /\       /
|           R1   /  \     R6
|            \  R3   R4  /
|             \ /     \ /
|              o       o
PS             |       |
|              R2      R5
|              |       |
o--------------o-------o

Where "PS" is the power source and "o" is the nodes and "Rx" is the different resistors. Please Help.