Finally managed desired setup:
2 instances of JTAlert/WSJT-X and two active slices with Flex 6500 AND N1MM for dupe checking across different bands, callsign verification, etc. This required a third party TCP/UDP port splitter program. The secret (which took all day to discover) was splitting the secondary UDP server port and forwarding to N1MM. Splitting the main UDP port server interfered with JTAlert's operation (no alerts forwarded to WSJT). It's a less than elegant solution, but works for me.
The third party program was way too expensive, but I did manage to get a 50% 'educational' discount.
Thanks to Laurie VK3AMA for offering some help on how to open the second instance of JTAlert.