That worked, for changing the 'Send to Folder' preferences.
The different PC readers all read from only the folder they recognize --I don't see any way to change that. "My Kindle Content", "My Barnes and Noble eBooks", etc.
I had to change the default to "Send in specific format", because it insisted on sending in ePub format no matter what the preferences are set to. PRC, MOBI, ePub is the preference order, which is ignored.
Many thanks for the help.
I'd hate to have to talk someone non technical in setting this up for PC reader use..