I have a Sub with a built in AMP but it is too big for the boot (no surprise there)

Is there anyone here that could maybe modify the box making it smaller/custom fit and ideal for the S and still use all the components from the one I have?

 

I can't see it being all that effective so far back with a bulkhead inbetween? Even if you did manage to get it in there. Plus, the box will be designed for optimum output through shape and size.
Once you mess around with it you will probably lose some quality.
The previous owner of my S had an enclosed shallow pioneer sub fitted behind the passenger seat and in my opinion it's as power full as a bigger sub would be right back in the boot space.

Will.

 

There's no issue with the sound travelling through to the cabin but the speaker you have may have a recommended minimum space requirement so check that prior to cutting it down

My box is custom fit to hug the drivers side part if the boot

 

That is just what I want

 

I've got one but it needs a separate amp.

If you know someone handy (UF?) you could borrow mine to take measurements, I think you'll struggle to get the built in amp in.

 

My amp is tucked away inside the spare wheel so nothing is on show apart from the sub

 

It may be possible to remove the amp and speaker from the existing box, build a new (smaller) box for the speaker and then install the amp above the fuel tank or inside the spare wheel, or even under/behind the passenger seat.

That's probably the bast way to go about it.