If I'm understanding what you're typing, you've already found the calculator for how much sugar you need per bottle right? then all you need to do is divide your batch by the volume of your bottles (640oz/16=40 bottles) divide your sugar necessary to bottle by 40. Then use enough to prime 6 bottles. The calculation for keg priming is usually quite a bit lower but all you'd have to do is remove the equivalent volume of sugar for the 6 you bottled using the same method and prime your keg. Or, since it is a tripel and they're usually pretty effervescent you could just prime your keg like with the whole volume and not worry about it. 6 pints is only 15% of the total volume. It won't make that big of a difference.