Hmm, Is the Earth flat after all? If I travel far enough from the well behaved and most common color management scenarios, I fall into the bottomless "old school very expensive trial and error, hardcopy-proof, never get it right" void. Scary.
Have you tried converting your file to RGB and then softproofing? It might not be exactly 100% but I suspect it will be close.
Assuming the output device can reproduce a good grayscale, the second colour is Pantone and your monitor is accurate (and capable of showing the Pantone correctly) there is no need for softproofing. You only have two colours to worry about, your Pantone (which is predefined) and various shades of black ink.If the output device can't produce good grasyscale you'll have a colour cast, but that could vary depending on where in the delta E range the device is at the time of printing.All this assumes that your printing device is some sort of printing press.
Thanks for your suggestion. The real problem I'm facing at the moment is that I'm working with a presshouse that has (according their own words) very little experience with printing duotone. Also for me this is the first time for preparing duotone images for press. I had some test proofs made but most of them appear so far from what I'm seeing on my screens (sRGB and wide gamut, both properly profiled) or from what I get if I print them on my own printer that I really don't know what to trust. Actually what I see on my screen and what I get when I print the images on my own printer are quite close. But I don't know if Photoshop's color management knows how to simulate spotcolor dot gain and screen angles properly.The proofs made by the presshouse are made with an inkjet but I do not know what kind of rip they use if any and does their system predict dot gain etc better.Cheers,J