After reading what little I could find, surely one doesn't have to remove the ENTIRE rear deck to remove/replace the 2 speakers...
The grills look like they hook in on one side & snap down on their other side.
It's 11 yr. old, brittle, sunbaked plastic... Gotta be gentle.
Cant seem to figure out how the grills "undo"...
Help, por favor!!

 

The whole rear deck really needs to be removed as well as the rear pillar covers. Its not that hard but takes some time. Under the rear deck will be some small white plastic snaps that hold the deck in place. Just squeeze them with needle nose pliers and push them out. Volvo prides itself on being a pain in the *** to modify, but its worth it. I'm replacing my rear speakers with subs. I would highly suggest doing the same so you don't have to get custom mounts. Have fun

 

Deck has to be removed, a PIA job