Hey Richard,
The vifas i got turned out to be just chinese crap that had just bought the brand name.
I got them from jaycar and they were cheap, but I should have done my research first.
Below is a picture of the pods I made, but I'm sure a decent car audio installer could make and install some for you.
This was by far the biggest improvement to my system. I did one door first and then sat in the car playing with the balance and the difference was night and day - the volume almost doubled, the bass extended a long way and became much stronger, and vocals improved dramatically with better clarity and separation.
It was an effort to make the 6.5 in the front, and a 6 inch would be much easier but I wanted a 6.5 as I'm not running a sub.
A sub isn't really necessary in this setup unless you listen to alot of drum and bass etc.
In my opinion on all the e46's the weakest link is the speakers.
IMO first upgrade on a e46 would be speakers, second upgrade would be speakers + amp, third upgrade would be speakers + amp + head deck.
The factory wiring is not too bad, but its proboably worth looking at some cheap sound deadening and removing rattles.
Neals suggestion of using a four channel amp to actively biamp is a good one, although I must admit to not being a fan of class D amps.
Keep us updated, and good luck.