flex 6400 double rx

To explain further, you can only have a maximum of two receiver slices. In your initial explanation suggests you already have two slices open. A third, even on same frequency of first slice is not possible with 6400, 6400m, or 6300. Here is a quick breakdown 6300/6400/6400m - two panadapters, two slices, I SCU, and 7 mHz bandwidth maximum. Only 1 antenna can be active at a time. 6500 - four panadapters, four slices, 1 SCU, and 14 mHz bandwidth maximum. Only 1 antenna active at a time. 6600/6600m - four panadapters, four slices, 2 SCU, and 14 mHz bandwidth per SCU maximum. Only 2 antennas active at a time maximum. 6700 - four panadapters, eight slices, 2 SCU, and 14 mHz bandwidth maximum per SCU. Only 2 antennas active at a time. Also 2 meter receive. This table gives all the details. https://www.flexradio.com/comparison/ Dave wo2x