Once again, chatting with you all helped me solve the issue.
A couple things seemed to be needed for me to solve this:
1) I changed the Filter type to MIN_MAG_MIP_POINT. linear interpolated across the colors (which...is what it does...)
2) For my usage, I needed to switch the Addressing to CLAMP.
I don't know if this mattered, but I also:
3) moved the three Texture1D declarations in the shader to an array, and did the DSSetShaderResource as an array...this probably didn't change much but I /think/ is a better approach
Also, I double-checked all the channel values and hand-calculated a bunch to make sure that what I was seeing in the SaveDDSToFile call was in fact what I was inputting -- as it turns out the DDS viewer I am using is a bit weird and unreliable...best to just do the math by hand.
Now, the calculations all seem correct and i'm getting some interesting stuff being done using the 1D textures.
Thanks again (and double thanks to MJP who helped me out twice in 2 weeks!)