Hi Bert,
The IC6 is a great first foil for fast progression! I used the same. You definitely want to be downlooping on the gybe. Its all about timing the downloop with your turn speed to maintain tension in the lines throughout the manoeuvre. I built up a really consistent downloop gybe (with foot-swap) riding on a surfboard before even trying on the foil.
As for straps vs no straps it depends on what you want to do: i'm biased towards using straps as it takes you more down the race pathway. you can put more energy back into the foil through your tacks and gybes as you kick into the straps, plus having straps makes it way easier to deal with seaweed and do jumps.
Heaps of videos on youtube on how to gybe. I recommend watching this one from Daniela Moroz, it is pretty thorough:
cheers