Actually any 4 lines bar will work somehow, but to fly a foil kite you need to take into considerations the followings:
1. You need a bar which has the longest possible depower(bar travel) and therefore you would like the shortest possible chicken loop. The Infinity 3.0 is just like that. This inifity 3.0 chicken loop is not sexy at all but relatively short so the bar is quite close to you. This chicken loop is not ideal for unhooking but otherwise it is quite perfect.
2. Then you need to consider that most of the 4 line bars are not auto untwist which means that after a few rolls or loops you can probably forget your single line safety system unless you always untwist the line by hand.
3. Then you need to consider that sometimes you really need to do something with your control lines and you might need the balls as well. Actually the balls on the lines are just put at the correct distance so by catching those you can execute the best restarts or stalls, etc.
4. Actually to feel the foil kite you need a bar with an uncovered rope as the depower rope. If you try a depower rope which is covered with rubber or some plastic material you will feel way less feedback from the kite as those materials has way higher resistance then an uncovered dynema rope. I just tried a cabrinha bar for the Soul 15 and it was terrible.
5. Then for each kite has an ideal line lenght, so for the Soul 12 the 22 or 24m line would be too long unless you trying to ride in super lightwind. The 17+3 M line lenght of the Infinity 3.0 bar is quite optimal for Soul 12.
The Infinity 3.0 bar is still the safest, and best foil kite optimized bar which is mass produced. I am using other bars as well mainly for unhooking reasons and for tube kites, Kitech, Ozone bars, and today just tested a Carbrinha Fireball bar which I thought it will be very good for hydrofoiling but actually the bar had way too much restiance plus it had other problems too so it turned to be a very bad idea.
Dont belive to me
just try as many bar as you can.