Custom Window Sound Blockers

For very large windows/sliding doors, there are sound blocking drapery that is used in hotels/motels that can absorb some of the sound.  Search Amazon for sound proof curtains.

They should work as intended--another pane to block sound, the pane itself made of a non-resonating material, and a good rubber gasket for air isolation.  Also, acrylic is much better a passing light than is glass.  Only downside is that it scratches easily so one has to be careful about cleaning (only soft cotton towels-no paper towels or tissue).  

As for reflecting the sound in the room, at least you will not have to worry about the panel itself buzzing and it might absorb some high frequency energy.