Thanks I'll have to check this out.
At $209, the Kato SoundBox' price tag may seem a bit steep (it's currently in-stock,
here at MTS), but I never run my railroad without it! So to me, it's been worth every penny. I expected that I just wouldn't be happy with the limited frequency-range of an in-loco speaker, especially in N-scale, so I went with the analog-only Kato SoundBox very early into my re-entry into the hobby, specifically for its external stereo-output jack. I just knew that when hooked up to an external amp, this thing would rock, and it does!
I have two identical low-end Sony 5.1 surround-sound systems on my railroad. I bought both on sale for $150 each, and each came with four compact surround speakers, a small center-channel speaker, and an 8" sub-woofer (un-powered). Again, even the most modest external amp and speakers makes this thing sound awesome! The first system amplifies my SoundBox output, and the second system runs a Fantasonics' "
Big City Modern Diesel" ambient-sound CD. The combination of both (through two separate speaker systems) really adds a lot of atmosphere to the railroad. I highly recommend both!
The only other option I would consider (when I convert to DCC) would be BLI's Rolling Thunder DCC receiver and sub-woofer system. Of course, you have to have locos with with BLI's Paragon 3 decoders installed for it to work. But I would probably only run a single Paragon 3 loco, or two at most. Any more than one or two externally amplified locos would probably become an annoying cacophony of noise.