I don't think the depth is the limiting factor as their is only 4mm difference in depth between the 5.25" and the 6.5". The problem is in the total diameter that runs the full depth. The magnets and the supporting metal basket are huge. I was able to install the previous JBL 6.5" because they were shallow and the metal frame supporting the magnet sloped inward. The Hertz are almost the same diameter, like a cylinder. I can get pictures this weekend to give a visual because I know it's clear as mud.