Is an aftermarket sub install possible?

[Nigglepug]

Hi. I have a B7 Avant with the Bose system which has a small subwoofer in the boot. I want to add an aftermarket active sub for improved bass and wondered if this can be done and if the new sub can be wired into the existing wiring in the boot?
I have the RNS-E head unit which has no RCAs but understand that fitting an in-line converter would rectify this?
I have spoken to a couple of ICE companies and one said it's no problem to add the amp but the other said it's unlikely so thought I would ask here if anybody has done this successfully please.
Any help is appreciated, thanks.

[Nigglepug]

I'm looking to get this done before Christmas (if Covid allows) so any help would be very much appreciated, thanks.

[Steve Q]

I believe it can, but I'd get an auto electrician to do it. 

[Nigglepug]

Well, the answer to my own question is........yes you can install an aftermarket sub in a B7 and quite easily as it turns out!  I'm no auto electrician by any stretch but the way I did it is surprisingly straightforward so if I can do it, anyone can.

Kit used:
Vibe 400.1 mono amp (170W RMS at 4ohms)
Vibe Rapid Fit wiring kit
Audiobahn 10" downfiring 4ohm amp
14AWG speaker wire

I installed the amp (which is so compact that it fitted in the small shelf in the top of the glove box) using the Vibe Rapid Fit wiring kit, where the power cable simply piggy backs into a switched fuse in the fuse box (no need for routing a power feed from the battery through the bulkhead). 👍
A word of warning: do not use a constant feed as it will drain the battery (voice of experience!) 🤪

The amp obviously needs a signal to amplify so, as the RNSE head unit doesn't have RCAs, I tapped into the 2 wires going into the Bose sub in the boot and ran speaker wire back to the amp.
The amp has an auto sense feature so a remote lead is not required.

I partnered the amp with an Audibahn 10" downfiring sub as it was the best way of keeping useable space - I didn't want a large sub box filling up the boot space.

I'm really pleased with the result - plenty of adjustable bass. It hits hard if you are so inclined but personally, I prefer subtle bass filling the cabin and feeling the rumble on certain tracks! 

Please note: This was for the Bose equipped B7 - the non-Bose models maybe different?

Happy to answer any questions.