The weather finally broke and I was able to make a run with my new K-27 Bark Box under load. I pulled five JS cars with ball bearing wheels, which is not a particularly heavy load, but enough to challange the Bark Box. I plan to make a run with 30 or so freight cars later on and I'll see if there is any difference. The Bark Box worked as advertised and did not affect the steam plume. You can see and HEAR the run at:
What is interesting is to listen to a couple of your clips of th K-27 without the Bark Box so you can really see what hte difference sounds like.
Too late now, but I should have had a before and after run by. The best comparison is the second run by in my K-27 freight run video where you can barely hear the chuff. http://www.youtube.com/watch?v=ihD_JTB6Jco
It is the same locomotive, same camera and about the same weather conditions.