I tried this and couldn’t find any way of selecting either of the BL1611’s dual-inputs when the Beoport is also connected to ML. I tried various combinations of Beoport Option (0, 2, 4, 6) and BL3500 L.Option (0, 1, 2, 4, 5, 6) but had several conflicts as far as I am aware. At one point Beoport even locked up (the PC screen controls disappeared) and I had to do a complete re-install of the SW!
One should think this was supported as the official drawing from B&O shows the dual input, and a Beoport should be able to coexist with another audio master in the same installation. But of course if that drawing is before the Beoport was made things could have changed.