with quark6 you could turn off color management
with quark 7 and 8 you can't
I expect this is your problem.
One solution is to output As Is. If your document is entirely grayscale this would work.
A longer untried solution would be to try and change the Grayscale ICC profile to be just the black ink of the cmyk icc profile that your quark uses.
Start by opening Photoshop and go to Color Settings. Against Gray - the "options" are basically only various amounts of dot gain. Click on one of the values and you will see a drop down menu. Go to the top of the menu and choose "Load Gray". Pick the same profile you use for your CMYK space. You'll see it show up as "Black Ink - (profile name)". Now, click on it again but this time choose "Save Gray". Make sure you save the new profile in the same place as the other profiles you have. (kudos to Matt Beals for this)
Now select this "Black Ink - (profile name)" in quark's color manangement greyscale prefs see if it makes a difference.
... there was the puzzle of why the sun came out during the day, instead of at night when the light would come in useful.
Terry Pratchet