Vandersteen 2CE Signature Speakers

Hello.  I recently auditioned a used pair of Vandersteen 2CE Signature speakers. I found them to be amazing for jazz (lots of detail, great imaging) - really everything I read about on how these speakers sound.  However, upon listening to classical (full orchestral recordings of Mahler symphonies and Strauss tone poems), I found them to be boxy, dull and closed (quite the opposite from the jazz recordings).

Is this normal?  Why would this happen?  What can be done to fix this? I would like to buy them. 

Thanks