But the only other field on that page is the device which is already filled in with /volumes/MW IPOD and it won't allow me to change that to enter the correct /dev/disk2 entry.
Wrong. The device path is not to be selected, so /dev/disk2 is definitely wrong. /Volumes/MW IPOD could be correct.
Mac OS X apps will always understand anything under the /Volumes folder as a mounted filesystem.
That's wrong -- applications don't magically understand this, resolving the mount point to a device file (which is needed for ipodpatcher) is something that is necessary and is implemented in Rockbox Utility. The mount points offered are retrieved from the system, they are not related to some magic /Volumes prefix.
But in the device box it has autofilled in /volumes/MW IPOD
That "device box" is a dropdown list, and as such it needs to have an entry shown. That entry is not necessarily the correct one, especially if Rockbox Utility tells you it can't select the mountpoint by itself. Open the dropdown list and see which items are available. You should be able to tell from the volume label and size shown when opening the dropdown list which one's the correct one.
The preselected item is the one that had been selected in the past. It is shown
even if that mountpoint doesn't exist anymore. This is done for the case someone starts Rockbox Utility without the player connected. In that case you can simply connect the player, mount it (or wait for it to mount, depending if your OS automatically mounts it like OS X and Windows do), and then close the configuration dialog with "Ok" without the need to configure anything again. This assumes that the player will get the same mount point, but that happens in most cases.
I assume you did try to use Rockbox Utility before converting the Ipod to a Winpod. Then the configuration still has the mountpoint of the old Macpod "configuration" of the Ipod, and since the Ipod is likely to have a new label (thus new mountpoint, since OS X creates the mountpoint from the label) you need to select the new one. However, detecting the mountpoint is something that should work 100% reliable for Ipods. Since that doesn't happen for you I assume something is still wrong with the Winpod conversion. How did you perform the conversion?