Thanks, Mitch. It does appear I have the "s" unit after all.
But, that still doesn't explain how I get stereo and/or dual receive capability.
What I have can best be described as dual VFOs. In software, I can "throw" the output of either VFO into any combination of left and right with a slider.
How do I get that functionality replicated in the Mk1258IIs ? How, in other words, do I get both channels (L and R) delivered?