well it depends on the model of the speakers. Boston has a low end line that wouls not par up with the Kappa's but the upper end boston line's such as the pro's and the z's are much much better then the Kappas.
well i heard the Z6s and I have to say they sounded terrible and im a BA fan. now they had the tweeter mounted directly above the mid-bass driver so that could influence the sound but the ones i heard sounded so bad that i cant believe that the placement accounted for all of it. Id go with the DIAMOND HEX series over the BA PROs. same basic price and to me the diamonds sounded distinctly better.
They're optimized for off axis performance, they sound better in a car. I don't like their newer stuff as much as the old Pros and such, but it's still ok. I like the Perfects better than the Pros, but both are on the bright side.