@William.walsh0612 - Although this is primarily a homebrew forum, you are certainly welcome here. We are happy to help.
A shorter liquid line with higher pressure will contribute to foaming. There's a line length calculator here http://www.mikesoltys.com/2012/09/17/determining-proper-hose-length-for-your-kegerator/ although it's not specifically focused on stout.
Beer gas, as you probably know, is a combination of nitrogen and CO2 - the ratio of the two varies. You can ask your gas supplier what theirs is. The beer will absorb CO2 but not nitrogen. In a larger bar where the kegs may be a long way from the taps, and maybe even in the basement, the nitrogen provides pressure to push the beer all the way without over-carbonating it due to the higher pressure required. Its a balance of the gas ratio and the line length.
As others have said, reducing pressure will reduce foaming, but will also reduce carbonation. A longer line will also reduce foaming (Pressure drops along the line due to friction as beer flows.) If that doesn't work out, consider a beer gas with less nitrogen in the mix.
I bet your suppliers can offer specific suggestions.