is it possible to set up the 325, so you can use the disk with Windows without the NAS box?
My 325 uses ext3 for the data partition, and there are Windows tools which can read that. Maybe newer firmwares will use ext4, which is a bit more complicated, but still readable for some Windows tools. (UFSexplorer for instance).
But when a type 2.x raid is used, it can become more complicated. My box used type 0.99, which is transparent, but cannot be resized above 2TB. Maybe newer firmwares use type 2.x for that reason. Don't know if there are Windows tools which can find the filesystem on that.
And yes, as far as I know there is no conversion tool from ReiserFS to ext3/4, so changing the filesystem will destroy your data.