My amp which is much bigger in size than JL 250/1 is in the trunk on the right side, behind the side carpeted panel (adjacent to the fuse box).
I suggest, try another car audio shop....

Thanks for the follow up. My rear right side panel is design to "cave in" to allow for more storage in the cabin (i.e. golf clubs) etc. Is yours like this?

Also do you have any pics of your amp install?

So I did a lot of digging / looking today. Shashank Mittal, it appears that your amp is next to the battery under the hatch. Did you have to modify the plastic insert? If not, did you just remove the plastic insert that covers the battery?

Looking at your pics in your album (sweet setup btw) it appears that the crossover was mounted in side right carpeted panel or am I seeing it wrong?

Alright, I took some pics of my X5 and proposed area.

I had a few questions:

1.) Did you install your amp below the plastic protector?
2.) Is just removing the plastic piece an option? Is the only function for storage?
3.) Any problems with what I pictured below?

http://www.mindworks.net/bmw/1.jpg
http://www.mindworks.net/bmw/2.jpg
http://www.mindworks.net/bmw/3.jpg
http://www.mindworks.net/bmw/4.jpg
http://www.mindworks.net/bmw/5.jpg

I used the videos BSW has on YouTube for the subwoofer installation, wiring colors, which to tap, etc for my E53...do they not have the same for the E70? I wouldn't pay BSW's prices, but maybe checking out their site will get you the info you need...wiring colors for left, right and remote turn-on being the most important ones that you need to find. The problem with taping the wrong wires on the amp is that some may be controlled by the DSP, but for the subwoofer, you only want the signal that isn't filtered so you can let your aftermarket amp do all the filtering.

Thanks, yeah I think the pin-out is ok, however i'm just trying to figure out where to install the thing. The 250/1 amp is really good and I had it mounted in my side panel on my E53 however the side panels don't have enough space on the E70. Or I haven't figured out a way to mount it in there yet with the stock setup, so looking to put it under the floor.

I put mine in the left side panel like you did in your E53, but I've seen people flip the spare tire over and make a panel to mount it inside of the spare tire...once again on an E53. I've also got the sliding load floor, so the side panel was the easiest. Maybe underneath the rearseat, but I'm not sure the amount of open space in there in the E70 vs E53.

I have put in a powered sub but very unsure what are speaker cables can anyone tell me what colour cables are the subs . Am I right in thinking the amp is on left hand side looking at the rear of the car .
Many thanks if you can help

Can anyone elaborate on how to tap into the signal source?