Dual Voice Coil Subwoofer Question

You can't push an amplifier past its limits.  It is rated at 2 ohm stereo...that is MAX, (although it will work more comfortably at a 4 ohm stereo impedence).  2 ohm stereo is equal to 4 ohm bridged mono.

A 2 ohm DVC subwoofer has 2 voice coils each rated at 2 ohm.  These two voice coils should be connected on the speaker itself.  You cannot  wire them in parallel,  because it will wind up as a 1 ohm load, which your amp will not drive. 

So you wire the two coils in series, and the result  will be a 4 ohm load which you can bridge onto your amp.  Just connect the + of one coil to the - of the other coil.  Then connect the other + to the subwoofer +connection on the jackplate...do the same with the other -.  That's a series connection.  The jackplate will then provide a + and a - for connection to the amp as a 4 ohm load.

The 4 ohm load onto the amp in a bridged configuration will make the amp work as hard as it is capable of working.  That is what you are trying to achieve.

You would be better off forgetting about y-cables in this case.  There is no need to over-complicate your install to try to tweak out some magic "extra" power.  Manufacturers derive the power ratings in some different ways.  But an amp has a definitive limit to the amount of power it can produce.

Don't go by numbers.  Just hook it up right and enjoy the sounds.