There is a yahoo group for Designer owners.
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's a ton of mail on that group [which drives me crazy] but somebody will always respond to your questions. The format that you choose to download depends upon what kind of software you have installed and how many formats your software recognizes.
When downloading a design, I have always been advised by my Viking dealer/instructor that .dst is the best format to download into your software because it is truer to the original design. However, the colors are lost and you have to program them in. Most of us who use embroidery software end up tweaking the colors anyway, so it's not too big a deal.
When you write your card using the software, the software changes the file suffix. Even though I work with many design formats, when I use the card writer/or disc writer, the format always changes to.shv on the floppy disk but I am unsure what it turns into on your QDII d-card.
Your dealer should be able to answer your question as it pertains to your particular machine. Janet Wilkinson