CorelDRAW X4 :: Importing Illustrator Files

I work exclusively in coreldraw x4 but am need someone who works in illustrator, which means they need to be able to open my files, work on them, send them back and then i need to be able to open them in x4. don't care what file types are involved as long as i end up back with a .cdr file that still has all the important info like groups, font details, accurate cmyk values, lenses, pattern fills and gradient fills intact. etc.

since i also have illustrator on my machine i thought i'd do some tests to see if this works and here's what i've found:

1. cdr files saved as ai seem to open perfectly in ai with the exception of color changes in pattern fills. (they look essentially the same but CMYK values are oddly different.) they stay in the altered cmyk values coming back into corel.

2. coming back to corel some teeny tiny amount of info just plain disappears (in this case, some outlines)

i've tried bring it in as a pdf file and ai (and yes, importing both times) but still the issues.