I think the TAD Ref-1 is a nice alternative.Same price range too.It has the distinct advantage of a dual concentric midrange/tweeter,and constructed with berrylium.Stunning clarity and exceptionally coherent.Also,it employs two "ten inch" bass drivers(not beryllium here),which though smaller than the Isis' bass drivers,are constructed in a brilliant way.The rubber surrounds have multiple folds,and allow for very large excursions,with amazing linearity and detail.A MUST to audition,at this price range,and a brilliant design.
Good luck.
Good luck.