is there anything that I can add inline that would raise or lower a speakers impedance? sum sort of resistor, coil, nuclear reactor,flux capacitator??

The problem:

4 ohm DVC subs x2
mono amp only stable to 2ohms

Was told I should not simply hook up only one voicecoil per sub

Connect the voice coils of each driver in series and then connect the two drivers together in parallel. This brings you back to a total of 4 ohms.

not sure how readily available they are, but, look for Stinger/Veritas Accumatch Impedance Drivers. they should do what you are looking to do.

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I would build a box for one sub and run it at 2ohms. It should be louder than 2 subs at 4ohms. If you still want to run both subs then I would run them at 4ohms. If you run any resistor wether it be in series or parallel it will dissipate any extra power you get as heat. the subs would see the same power with or without the resistor. I don't recommend wiring 1 coil per sub either.

theirs was a thread like this on the12volt, and i from what i remember the consensus was that running just one coil was ok you just couldn't run as much power, i dunno for sure, you can go looking for the thread, it was decently long one i think.

the problem is, the overall rms is halved, as well as the t/s specs changing substantially.

some subs are meant to be ran this way as one coil is designed to be a ballast and effect the t/s specs as needed.

i would not run one coil under any circumstance.