It’s difficult to visualize your set up so please let me know if I’m a bit off with this.
You can use event instruments with loop regions for each of the 8 bar/6 bar instruments. Have a loop region within the two event instruments’ trigger regions to ensure they aren’t getting untriggered/retriggered.
Otherwise, if you use two separate async instruments with infinite looping enabled along with a loop region that stays within the trigger region for both instruments, they should both loop independently.