They are good for orchestra(classical) as well for sure. Electronic orchestration... I think it will sound pretty badass on ws99
With the lively mids and the bass nothing can go wrong. But you might want to consider ath-ad900x(I just got them) as it has wider,airier soundstage and excels in orchestral music due to its open-back nature. While it doesn't have the thumping bass of ws99, its not bass light either and can be made better with good amps.
Build quality, I'm probably the only person who's got a build prob with ws99, the right swivel came loose and fit went slightly off although I kept them in a hard case while on the go. Strage but hopefully not many will experience this.