Mono center speaker in unused rear channels

Hi

My stereo consist of a standard 4x50 amp and two 4x6 speakers in the door pods. I am not going to use the rear channels as I don't want to destroy the parcel shelf, and am not keen on portable speakers.

I'll probably buy a powered sub at some point, but wonder if an extra center speaker in the original dash mount would fatten up the sound? I was thinking it could be wired mono in the rear channels in order to be adjustable. Would I need to hook up an extra resistor in the rear channels to avoid impedance issues if so?

Could you not fit under seat speakers, or modify some BMW under seat subwoofers?

Yea I'll try out an under seat sub first and see if it helps.. Looking forward to a 5th gear also, will hopefully  be able to actually hear music now lol.

Would have been cool to fit a center speaker in the original dash mount though

In theory yooou could stick a centre speaker in and just hook it up to either the left or right channel.

Problem is you'd lose the 'stereoness' as it'd be only one channel. Plus it's only a small speaker anyway so it wouldn't add any depth to your sound and as there is no 'cabinet' for it to be in it would actually be more tinny overall.

Stick in a sub and use a cross over to remove the lower frequencies from the front speaker  

Ian