I have a web article about making a dcc soundbox at:
http://www.pacificcoastairlinerr.com/1879/soundbox/
Harold
Nice Job.
Have you seen the MRC Synchronized Sound Box for Steam and Diesel. Can be used for DC and Dcc.
Bob
Not worth the money. Bought one for my dabbling in N scale. It is MRC. The diesel works fair. I had sold the diesel decoder in the article and didn't want to invest in a Soundtraxx so I bought the MRC. Works ok with my N scale scenic ridge gives me sound.
The steam can't be synced just like the other MRC DCC decoders. The Tsunami is the only way to go for steam.
Harold