Sorry eddie and rocky, I have to disagree. Trusses are made light weight, and normaly end bearing, he has to offset the weight of the beam plus any other material or live load on top of that. Also they will not give any more lateral support than cable would since its going to be a thru-truss.
The cable if done right, there would not even be any bounce, considering the weigth of a person jumping (live load) will be a fraction of the actual tension on the cables, and it would never need adjusting if you use the proper size cable.
Keep in mind, the same load that would be needed on the cables, depending on the angle of the cable, the truss turns this load completly horizontal. This tension load now is transfered into the top rail.
I will agree with eddie on the point that if you had any beam left for the underside and did as he said, it would do the trick, but i dont beleive that was the "look" you were going for. How far you get the beam out will determine how much bounce you will have at the end.
Sorry, one other thing, the cables will need to be attatched to the columns independently, as I beleive you had done.
