But, exactly as you stated, everything seems to be working thus far. Once again, thank you for your help and patience!
As a review (in case it helps someone else with a similar situation or who is similarly knowledge-challenged), here's a summary of what I did in order to allow the MXF file to be stored on a NAS and accessed by client HTPCs from that central location.
1) Wrote a batch file that copies the MXF file from the EPG123 Server to the NAS location (here's mine as an example)
@echo Copying Guide Data to Network Share
XCOPY C:\ProgramData\GaRyan2\epg123\output\epg123.mxf \\NASNAME\MXFFileDirectory\epg123.mxf /Y
@echo Process Complete!
2)Configure Task Scheduler to run that file after the EPG123 Update task runs (I set it for 30 minutes after)
3)Create the scheduled task in each EPG123 Client (in Client Mode), pointing to the MXF file stored on the NAS using the UNC (NOT Mapped Drive Letters) Path
4)Within the task in Task Scheduler, under the General tab, make sure that the "Run whether user is logged on or not" radio button is selected and that the "Do not store password..." option is UNCHECKED. After you press "OK", you will be prompted for credentials that allow access to the MXF file on the share.
I think that's it. Seems so simple in hindsight.