I would agree with MDS that it's better to concern yourself with the SOUND first, then of course specs, build quality, aesthetics, everything else that goes into the decision, rather than where each speaker sits in that company's respective line. B&W's absolutely lowest level speaker, for example, will still sound better than some other companies' very best offerings. That shouldn't be true against a good company like Axiom of course but it's still a valid point.
I haven't heard Axioms but I'm very familiar with the B&W 600 series and I can tell you, there is NOTHING "bottom of the line" about either the 603s or the 604s. They're both great speakers. A lot of their Nautilus technology has found its way into the 600 series 3 line and it's great stuff. Very well engineered and put together, and I love their sound. They're not the best speakers in the world and quite probably not even the best at their price points, but they're a very valid choice and for many people they're the right one.
By the way if you check bwspeakers.com you'll see that the 600 series isn't NEARLY their bottom line range. Below them there's the 300 series, then a whole variety of smaller or special purpose lines designed for different applications or for those who want the B&W logo on their HT speakers but can't afford the really good stuff. As I said, much of their Nautilus engineering has trickled down to the 600 series and actually I think by moving down from the 700 series to the 600, you're giving up more finish and aesthetics than sound.
Definitely compare them to the Axioms if you can, and if you get the chance you might also consider Swans or Rockets (both ID brands). And of course a lot of people prefer Paradigms to the B&W 600 series, though I personally do not unless you move way up to the Signature Series.
Incidentally I'll actually be comparing my brand spankin new set of Swans 5.2 (I had them delivered to my engineering partner's house for just this purpose) to a set of B&W DM604 S3s tomorrow evening! I probably won't get to post any thoughts on them tomorrow but I will be very soon, in case anyone's wondering how they compare.
