Adding a subwoofer and amp to 750i with B&W

[htdhvy]

Hi all, quick question.

My new 750i should be here end of the month. I ordered it with the B&W sound system. The one I demoed sound rather good (nice clean highs and mids) but bass was a little lacking for my tastes (I have the B&O system in my F15 X5 and am a huge audiophile in general).

My question - does anyone know if there is a preamp line out somewhere in the system where I can add another amp to power a subwoofer? I want to avoid tapping into the speaker level outputs and go for a cleaner source. If there is no line level output is there a digital one that I can tap into and add a D/A converter and then go line level into an amp?

If no to both of those any thoughts? I tried searching online and on the forum but couldn't find anything on this for this particular sound system.

Thanks in advance!