Hi Jak.
Thanks for the very detailed response. Heres what Ive learnt. I sorted tried what you recommended, instead of running a long speaker cable to the rear speaker, i got one of my bookshelf speakers from my house and connected that to the rear output from the new headunit. I was shocked to hear exactly the same "bass only" sound coming from the book shelf (its rated at 8ohm) so I thought there must be some setting in the headunit that would cause this. I then found a setting sony call "Rear Bass Enhancer" this doesnt enhance your bass in the rear, all it does is turn off any mids or treble from getting to the back speakers!!! so lamn. So, now that I discovered that, I tuned it off, plugged the bookshelf back in and low and behold, full range! re-wired up the rear speakers, and its now full range.
I think the biggest issue I have it seems is the technology of sound in cars has changed so much since I last really paid attention. It seems that the front speakers are now the most important set as they build the sound field up from them to mimic the idea of how you have your speaker positioned at home, this seems so bloody obvious now, but I used to always have the sound biased to the rears.
Guess its just something Ill have to get used to.
Either way, it seem the bypass works as it should, its just me being an idiot! Maybe Ill change out those rear one day to get some better efficiency out of them (they seem a little underpowered)
Was thinking of these from Polk MM691 (although they are rated at 2.7Ohm, maybe dangerous with my headunit) or the DXi690 (rated at 4ohm)
with a range of 30hz-25khz (94db) and 35hz-23khz (92db) respectively they seem good bang for buck (round $190 a pair)
Thanks for your help!
dave