Subs
You're going to get the best results if you keep things simple. One sub in the stock location will keep the phase problems to an absolute minimum. If you have a box firing at the rear of the trunk there will be phasing problems introduced. Trying to get some volume/airflow through the stock speaker hole (if you've removed the stock sub) is not too easily done and you may actually encounter hissing noises...port noise...from all the airflow.
Remember that the Vel controller has a setting for free air config...and it does it well!
You really can't change the settings on the stock crossover. That's built into the amp and from the last time I saw the amp, the crossover was DSP controlled, at least for the sub anyways. No passive filters anywhere for the sub! The Vel has an onboard electronic phase and crossover controller though. Just switch it to the point where it sounds good to you.
Get rid of the installer that wants bandpass in a SQ automobile! He's an SPL traitor in disguise!

Percy
Also looking at Phase Linear Aliante Subs....small mounting depth....euro mag said it beat out the focal utopia subs...pretty interesting.....you can find them at www.ampmanaudio.com
I'm almost finished with my system....Just waiting for my Mcintosh x-overs and controller to arrive...they're on back order....
I will post pics on my install......I'm sure it'll help to some degree
I don't think it's a good idea to replace those kind of subs with the factory. the orion sub is "meant" to use with a sealed box. the stock subs is open so if you put the orion sub in it's not going to sound very good.
I wanted to replace factory sub before too but decided to do the whole system. however if you want to replace "just" the sub JL audio makes a sub that's meant to use in an open space.









