Also, there’s a feature suggestion to allow both Plex guide data and XMLTV files, but it’s not very popular (9 votes in two years). You may want to vote for it:
I think there used to be some hack-ee ways to do this, such as opening two tabs to your Plex server and adding the two tuners at the same time. I have no idea if that still works and it certainly isn’t supported.
The best method, as @TheLivingBubba suggests, is likely to use a proxy tuner.
