[V8] Activ speakers

[pdlord at talent.com.au]

I want to fit an OE head unit in my V8 to give it an original look. I don't look
for hi-fi in my car, so I just want something that works ok. Here in Oz, Audi
shipped the cars in with Audi speakers (4 ohm?) and fitted a Pioneer deck
locally to save on import duty. So you don't see any factory Audi decks out
here, and the 'original' Pioneer was stolen and replaced by the PO with a newer
Pioneer version that has a million small buttons - which I don't like.

I've been looking at Ebay Germany and a few Gamma CC radios have come up with
'activ' speaker compatility. Anyone know what this means? I've tried googling
but have not come up with an answer.