Well I think we have a winner! I'll need to check with Lee and will post the winner's name once I have, but in the meantime, here are the answers:
1. What was Bang and Olufsen's first quadraphonic receiver?
Despite its more modern appearance, the BM6000 predated the BM3400. Answer BM6000.
2. Which was the B&O cassette deck that was first fitted with HX-Pro ?
Beocord 8002 - the 9000 was introduced at almost the same time but luckily no-one argued that!
3. Name the speakers that were shaped like a cube.
Beovox 2500.
4. Which speaker had 7 drive units?
The ones I know are the Beovox 5000 which has four 2" tweeters, two midrange units and a large woofer.
5. B&O's first colour video recorder was a V2000 type machine. Which was the first VHS machine?
The VHS 80.
6. Name the FM only receiver which had a caterpillar type control mechanism.
OK, this was a little tricky. Lots of BM1700 but in fact that had AM as well. The FM only version was black and called the BM1600. Seems more common in the US.
7. Which were the headphones available for the Beosystem 2400?
The U70s. And no, I don't know where you can get new ear pads! 
8. A remote control with a transparent display is a B&O novelty. Which one is it?
Beolink 5000 - very clever idea and especially as if works both way round depending on function.
9. Mythical black fronted top of the range receiver from 1979.
Of course not so mythical now!! We found one! The Beomaster 4401. Pictures are on site!
10. The largest slide rule receiver made - in its first incarnation.
Beomaster 1200 - was replaced by the black 1001.
11. B&O's first production colour televsion with a 25" screen.
Surprised this caused some consternation - Beovision 3000
12. B&O's broadcast standard tuner.
Beomaster 5000 - part of the Beolab 5000 system. It has variable inputs so that it can be used in a broadcasting station.
Well done to all of you that took part. The final answer is: 1,666,980,000 .