Originally Posted by grokit
my main concern is that as my 325is already have aluminum chambers
The SR325 & MS2 are a plastic construction similar to the lower end grado's. If you open a MS2/325 you will find a plastic assembly which holds the driver and completely covers the aluminum surfaces. The SR325/MS2 plastic inserts are the identical to ones used in the new SR60i, SR80i, SR125i, and SR225i.
The Magnum mod replaces these plastic parts with aluminum versions- making a fully aluminum air chamber. Whether or not you use a SR325, MS2, or SR60, every magnum shares the same aluminum chamber (+ upgraded driver) and therefor all benefit from similar improvements in sonics.
As you can see, only the MS2i's outer earcup is aluminum. The parts fit together to create a plastic chamber encompassed by an aluminum shell.