I still don't understand you. The remote devices are not "path related" nor are they identified by a "drive letter". Each device is identified by its own network computer name, which does not change.
well that makes two of us (who don't understand)
I plug in a device (a sansa clip+) and it shows up in windows as drives D and E (because it is in MSC mode rather than MTP as then it can be plugged into many devices and "look the same").
I go to the jriver handheld options and it presents a dropdown that includes "Sansa Clip (D:)" (the internal storage) and "Sansa Clip (E:)" (its external storage).
Alternatively I can go to "device management/add device" and the "device" is simply a path picked via an explorer file selection dialog
I have multiple physical instances of these devices and they present the same way.
Note that when I reference them being identified by a "drive letter", I am referring to how windows presents the device. I plug it in and it shows up as D and E and jrmc exposes just that. For better or worse, for a jrmc user, I don't use windows much so have no real idea how it selects drive letters/paths other than it appears to be "use the next one" (unless it's a mapped drive). My mindset here is linux based (e.g. fiddling udev rules to do stuff when you plug things in, a deeply unfriendly thing to deal with but still)