Ok, I just have to bump this thread AGAIN.
I've had my Intravee II installed for a little while, not long, and was already impressed by its features, even though I've not finished my navigation retrofit yet. I STILL have the HK BMW Business single-line CD head-unit.
I upgraded to the latest, greatest firmware today. You need a good USB to serial cable to do this properly, but I found a way to circumvent that using older hardware and.. uh.. less than sanctioned techiniques which are outlined here.
After the Intravee II rebooted with its new firmware, all I can say is WOW. Seriously. Ian was right, if you could choose ONE mod, and ONLY ONE MOD for this car, I would not hesitate to suggest this small device. The potential is.. limitless. That is a BOLD statement, people. Make no mistake, I'll own those words.
Even with my single-line display, I can already see that such things as correcting the speedometer, determining specific OBC functions/readouts, etc.. and even a small line that said Acc: +0.000G and Brake: -0.000G was available. (the car wasn't running)
People, seriously, do not walk, but RUN to support this small outfit from the UK. These devices are revolutionary for the E46 M3. To even remotely suggest that the DICE or Denison ice link have anything within a decade of the Intravee II is pure blasphemy and indicative of sheer and utter ignorance of what's exclusive to Intravention.co.uk. I owe nothing to them, am not their sponsor/supporter, do not peddle their products (can I? Please? It would be so easy to sell their products!) and only bought a used unit to satisfy my own curiosity. I have no problem stating if I make a bad purchase and can swallow a buyer's remorse pill no matter how large it is - it'll never happen with this device. Ever.
I'll never go back. Now, not only do I want the navigation -- I NEED it. The fact that this is actually an iPod interface is just the icing on the cake. Knowing what I know now, I'd have purchased it even if it did NOT interface with an iPod.