I have a room with 10 low voltage lights that are within their own metal boxes in the ceiling. Preventing sound transmission to the upper level is important. Should i consider taking the boxes down, building a box around it ( as seen on this forum) and deal with the plaster destruction with another layer of sheetrock?
What about covering the opening of the low voltage lamp with a circle of heavy glass ? ( not sure how i would connect)

fyi - I have spent the last few months getting an education on this site and am now ready to think about how to finish my HT room.

Sorry I can't help with your main question, but I wouldn't add a lens to the lights because you will probably run into overheating problems.