How to fix iPhoto 11 print quality

My wife scrapbooks our photos, and has recently upgraded from her old computer to a brand new MacBook Pro. She is a big fan of "if it ain't broke, don't fix it", so has been using iPhoto 6 on MacOS 10.4.11 on her old computer. She now has iPhoto 11 on MacOS 10.6.8.

The problem is when she goes to print a photo, the quality is much worse than it used to be. We are using the same printer (an HP PSC 2175 all-in-one), photo ink, and photo paper as before, and printing the exact same photo, selecting the correct photo paper and "Best Quality" in the print settings, and the comparison is laughable. The overall color is dingy/yellow/darker compared to the old print.

I'm hoping that there is some setting (or multiple settings) that were introduced or the default value changed inbetween iPhoto 6 and iPhoto 11 that is causing this difference. Can anyone tell me what I can change to make it print out good photos again? Or suggest things to try?

In the print dialog box, we have already tried changing the "Color Matching" preference from "Vendor Matching" to "ColorSync (automatic)" and that didn't make a noticeable difference. We looked over the options listed under "Real Life Digital Photography", but nothing seemed to jump out at us as a likely fix, and I am reluctant to keep printing out photo ink to try each setting individually.

— Update 8/7/2011 —

I have tried printing the same photo on our Epson Stylus NX420. We only have plain paper for that printer, but when I select the plain paper / best quality setting, the photo is the correct brightness in the lighter areas, but the other colors have a strong blue tint compared to the original and the HP print.

I have also printed the same photo on the HP printer from Preview (by dragging the thumbnail to the desktop and then opening that). That printed out better quality and color matching than the same settings using iPhoto 11 (I tried both plain paper and photo paper, with the appropriate settings), and also had the added benefit of not auto-cropping my 4×6 prints. However, the pictures were more pixelated than ones printed from iPhoto. Always something! 😛 Maybe iPhoto is doing some sort of smoothing filter, and that is why the colors are off?

I reconsidered my reinstall iPhoto 6 idea (either uninstalling iPhoto 11 or in addition to it). I have verified that it should work on Snow Leopard, but I know the iPhoto Library is already modified such that iPhoto 6 will not recognize it. Perhaps I could just have her import the pictures she wants to print into the iPhoto 6 library in order to print them, that wouldn't be terrible if it worked.