QTR-Quadtone RIP

I have used QTRgui for a while in the WinXP environnment, before
giving up not long ago, as my prints never matched the softproof,
altough I was quite pleased with the results of the prints. What
bothered me quite a bit was the fact that I had to do quite few proof
prints before being able to get what I have on the screen.
However, reading the last messages in this group, I now got the doubt
that I might have a flaw in my workflow. 
Then, I would appreciate very much if the experts here would check out
my workflow.

In the following, I assume I have already created the curves for a
particular printer/paper/ink combination within QTR.

Part A): Profiling
1) Open in QTRgui the 21-step (untagged) gray chart from QTR's Eye-One
folder and print directly from QTRgui (WinXP)
2) Read the 21 densities
3) Use QTR-CreateICC to generate an ICC profile to be used in part B)
for softproofing

Part B): Editing and printing
1) Open in PS CS2 a tiff immaged scanned with a Nikon 5000ED
2) Assign the profile gray-lab
3) Edit at will
4) When editing is complete, duplicate the image
5) Switch on softproofing for one of the two images, by using the ICC
profile obtained in part A). In the softproof setup, use perceptual,
BPC, Simulate paper color and simulate black ink ( I have tried other
combination of the switch, but this seems to work the best)
6) Add a layer curve to the sofproofed image and adjust until it
matches the non-softproofed image
7) Save the file (no further profile conversions)
8) Open the file in QTRgui
9) Print

The workflow looks straitghforwad. However, the print never matches
the screen. The only thing that puzzles me a bit in my workflow is
that I use an untagged file (21-step.tiff) in the print for the ICC
profile generation while I use a tagged file (with gray-lab assigned)
in the final print. Where the softproofing get the information that my
working space is a gray-lab?

Thanks,
  Daniela