CMYK coloring in Xara

[Toonicorn]

Hi, all!

I'm in a bit of a pickle here. I sell t-shirt designs from two websites, both of which are just fine with printing t-shirts using designs in RGB PNG format. But recently a friend of mine ordered a design from me and took it to a different printer (she wanted the design on a particular type of t-shirt that uses "dry-wick" fabric), and that printer wants the design in CMYK colors. They said they could convert the design themselves, but there would be a color shift. Well, I attempted to convert my RGB-colored design using Xara's ability, which requires exporting it in a TIFF format and setting it in CMYK. There was indeed a color shift. Not a great one. I'm trying to work things out with my friend over this, but this kinda sucks. Is there a better way to convert RGB to CMYK (I can't use my Photoshop Elements because Elements won't convert RGB-CMYK) in Xara to help the color situation (I don't like the conversion to TIFF because it doesn't have a transparent background when converted, like PNG does)? And in the future, when I color my designs, how do I do that in CMYK format (my manual for Xara makes no mention of that process)?

Thanks for any advice you can offer!

P.S. ALSO - I'm needing to export this file in Adobe Illustrator (AI) format - but the file's pretty big - how do I reduce the file size below 25 MB in Xara before exporting it? Thanks so much!