I've seen the AV8 bar. It doesn't give you more depower travel. It just gives you less pressure on the depower line. All that extra line is taken up by the 4:1 pulley system.
Most 4:1 race systems don't actually give you all that much more trim to pull, just less pressure on the line.
That makes sense for racing when you want to do micro trim adjustments while riding cranked over at full speed.
I wanted more depower. I still have the 2:1 system but a heap more travel. I don't find pressure on the 2:1 system a problem. I am tall with long arms and I can reach the trim line fairly easily. I am more of a free rider so I often do trim adjustments around a transition when I'm upright.
I've also discarded the little handles and velcro and magnets that companies put on trim lines. A single length of rope with a couple of knots in the end works fine. When there's a lot of trim pulled I drape the loose end over the bar. I can reach it and adjust it without moving from my riding position. If it's not draped then it just hangs down. If I was racing I could simply have a longer end on the trim line so I could always have it close to hand.
PS It's a fantastic feeling to have an unfeasibly large kite, foil cranked over, locked in and charging upwind. The race kiters are like that all the time. My pretend race gear is a close enough approximation without going to the cost of the specialist gear.
PPS My home modified Carbinha bars are nicer than the AV8 add-ons. I replace all the rope and bungie components and upgrade and colour code them. The first bar was made from Cabrinha and Ozone spare parts, now I just upgrade the newer Cabrinha bars.