Try turning up the pressure to 12 like usual. Sometimes foaming is the result of CO2 coming out of solution in the line and the solution is to actually turn up the pressure.
Other possibilities include: it's overcarbonated, the beer is warming in the line, the line is too long, too short, too narrow, too wide.
Long, boring books have been written solely on the subject of draft systems. As I'm sure you know, it's somewhat of a black magic getting it to go right, especially with homebrews of various gravities. I'd try to just keep changing things slowly and one at a time. Also, sometimes a bit of patience is in order. Mine often start pouring better after a day or so spent at dispensing pressure. When you put the beer under high pressure to carbonate and then release that pressure to server the beer, a lot of CO2 comes out of solution and results in foam in the keg. Sometimes it helps to let that settle down.