Yeah, I don't seem to have a problem with my two tap tower either. What does the off-flavor taste like?
Issues I'm having I think are coming from down in the keg, not the lines. I'll be replacing my lines soon with 10 feet lines. The 6 feet ones I have work well, but I want a little less foaming, so I'm going longer.
So the length of line that is needed has a lot to do with the type beer you are dispensing and the pressure that you are supplying it with- 10 ft seems like a lot in a direct draw set-up like a kegerator. Micromatic has a calculator on their web site to find out how long your line should be based on the tubing ID, # of restrictions in your system, volume of co2 in type of beer, temp of box etc. It is a bit of math but yoiu usually only have to do it once.
There are a lot of factors that can lead to foaming issues for example too low a co2 pressure allowing co2 to come out of solution in the line, too high a pressure causing beer to become over carbonated in the keg ( especially true when the beer is very cold and able to accept more co2), kegerator temp too high etc etc. I agree that sanitation is paramount ( I never want to drink am "accidental Belgian sour") but I have seen commercial locations with visible gunk in the 3/8 line from the keg to a jockey box that pour just fine. I think for sanitation/infection issues to contribute to foam they usually have to be coupled with other conditions.
For single or dual keg boxes I have found that a good starting point is 3/16" line of about 6ft at 12-14 psi and a temp of 34-36 degrees. For most beers.
I had never thought of using copper tubing going up the air supply of the tower to help the cooling function but it makes perfect sense. I would/will try zip tying the lines direct to the copper section of the air supply next time I set one of those boxes up.