Any other ideas?
Photoshop uses its own CMM ("ACE") whereas C1 uses the systems CMM (Color Sync resp. Apple CMM on MAC). Both CMMs produce almost identical results. However ACE uses black point compensation for the conversion to the monitor profile whereas Color Sync / Apple CMM does not (even if you set "Apple CMM" in Photoshop this does NOT apply to the monitor view - only to all other color space conversions).
Now if your monitor is calibrated and the black point stored in the monitor profile is not L*0 there may be a slight difference in the darkest tonal values.
Check this: compare the C1 preview to the processed TIF opened in Apples "preview" - they should match dead on.
You can also check this: use the standard monitor profile provided by the manufacturer (which has most likely a black point value of L*0) - C1 and Photoshop should match.
If they don't match even in these tests there's something else going wrong.
But if they match there's nothing you can do... the BPC in Color Sync and Photoshop is simply different.
Create a support case at Phase One and put in a feature request for a switchable CMM in C1 (so that we can utilze "Adobe CMM").
I know they are planing to incorporate a switchable CMM long term (I know as I was asking for this feature a while ago). However it probably helps to speed up things when many users ask for such a feature.
here a comparision of screenshots - preview|capture one|photoshop - with the calibrated monitor profile (black point is not
and here the same with the manufacturers profile (black point is L*0):http://drop.io/gbu95jz/asset/werk-jpg
(click on "download" to see the images fullrez)