It seems to me that a way of avoiding loss of sound quality due to that "less than optimum location", and sparing the panels from my bodging, would be to sit a pair of bookshelf speakers on the parcel shelf, pointing up and out straight at your faces. With a little luck, that should compete rather better with the lion-like roar of her mighty 948!
Has anyone else tried this?
Is there any reason I should be chary of connecting, say, a pair of these http://www.argos.co.uk/static/Product/p ... PEAKER.htm to, say, http://www.caraudiocentre.co.uk/product ... -23105.htm? (I won't necessarily be using these particular ones, or going to these shops, but the wattages match - which I assume is the limiting factor?)
If there's no compelling reason not to, I hope I'll be giving it a go - though using the living room speakers to start with, and getting a second set if it works. If not... no problem, nothing spent on speakers yet and I can take the conventional route

Tips on wiring in head units etc. welcome, of course, though I've a VHF enthusiast-friend lined up to help with that aspect of installation: you should see *his* car's radio setup...