No, this can not be done. You must have your AT5-files on a seperate card. As you might have seen already, you have two standard choices as mapping-source in the Menu of your unit: Lowrance or Navionics. But there is no choice as to what sort of files to use/ read. This is because the unit automatically searches for the correct files, depending on what map-source you choose.
So it will never look for AT5-files on a Navionics-card, and thus it will not work. :)
Way back, on older models like Globalmap, this was a bit more manual. Even if using a Navionics-card you still had to tell the unit where on the card it should look for the correct files. This was a bit of a hassle, especially when moving from one area covered by certain files, to another area covered by other files. So todays solution is much better, but it also means you can not "fool" the unit into reading other files then what the card or settings is telling it to read.
Units with two cardslots (ie HDS) can display two map-sources at once in splittscreen, bit the files still has ro be om seperate cards.
