Having owned the Onix Ref 1 bookshelf, I'd say it was at least the equal to my brother's B&W Nautilus 805--probably better it in terms of musicality. I don't think the B&W 602 has the refinement, top-end extension, control and tight/solid imaging to compete with the Ref 1 at all. I gave a pair away to my brother-in-law.
Having said that, I currently owned a pair of Usher Be 718. From what I've read, I do not think the Usher S-520 is in the same league as the Onix Ref 1. By the way, you can take it up a notch or two by upgrading the crossover caps on the Ref 1. I did and it was more refined and more enjoyable. The drivers on the Ref 1 are really special in my opinion especially for the used price.
Good luck,
Kenobi
Having said that, I currently owned a pair of Usher Be 718. From what I've read, I do not think the Usher S-520 is in the same league as the Onix Ref 1. By the way, you can take it up a notch or two by upgrading the crossover caps on the Ref 1. I did and it was more refined and more enjoyable. The drivers on the Ref 1 are really special in my opinion especially for the used price.
Good luck,
Kenobi