I just let the printer manage the colors. On the 4880 for media type I choose 'water color radiant white' and on the 9900 I choose canvas. I haven't had much luck with choosing 'photoshop manages colors' and then choosing a profile.
Not sure why you would expect consistency with this type of workflow. The best way to get printers to look like each other is to have a good color managed workflow, and letting the printers control the color is definitely not the way to do that. Any success you have had with this workflow is probably about tweaking things till they work, and you will have to tweak the file and printer settings again for the 9900, since they use completely different inksets and screening.
If you haven't had much luck with Photoshop managing colors, you should do some studying and understand why, because this is the correct method and will result in the most consistent and highest quality results.
I guess my questions would be why haven't you had much luck? What seems to be the problem with the prints when letting photoshop manage colors? What paper are you using and where have you gotten the profiles? When you let Photoshop manage colors are you making sure you have color management disabled in the printer dialog box? Are you profiling your monitor? Guess that's enough for starters.
