I just plugged in my new Kato Soundbox (above) with the included first-generation diesel Soundtraxx sound card installed (which has recorded sounds from EMD 567-series' motive-power). I'm not using the built-in speaker, instead, I've connected an old Sony surround-sound stereo system to the line-out output of the Soundbox (L, R, center-channel, and a sub-woofer, using a synthesized surround-matrix). My first reaction, once powered with the Sony amp and mini-surround speakers was, "Wow!"
The high-fidelity, authentic-sounding Soundtraxx recordings can't be fully heard or appreciated on the built-in speaker, but even a low-end stereo makes this system sound incredibly realistic. Add a moderately priced (e.g., ~$100) powered sub-woofer to your system for some really impressive low-frequency rumble! Even at idle, there's enough randomly generated sound to keep it interesting. The "start" and "sync" potentiometers are a bit difficult to figure out, but once configured properly, the box adds momentum features to the Kato controller.
I also plan to buy a second Soundbox, for which I can order Kato's third-generation GE diesel sound card (above), which according to Kato,
"[is] appropriate for multiple modern GE diesels, such as the P42, C44-9W, and AC4400CW" (I own a Kato AC4400). Of all the accessories I've purchased since re-entering the hobby, Kato's Soundbox adds the most dimension, offering a level of realism which really adds a lot of fun to your layout.
I just realized there are three Kato/Soundtraxx sound cards that I can eventually get which match my inventory of engines (among others):
• GE 3rd-generation diesel for AC4400CW.
• EMD 1st-generation diesel with turbocharger for GP35 (July 2016).
• EMD 2nd-generation diesel with turbocharger for SD40-2 (July 2016).
Next order . . . raised viaduct track!