This one fought me hard. I was finally able to get the speaker module and the LokSound select micro with EMD 567A 6cyl Full Throttle sound file all crammed in there. I am quite happy with the results. At 'Notch 3' there is a very strong 75Hz bass sound that you can see on the frequency analyzer. It plays 100Hz essentially flat. That is a huge improvement over cube speakers, which are the only other real option for this engine. This is about as good as it is going to get in this engine and I am quite pleased with the results. Here are some photos and a video.
***Note: You will need good speakers or headphones to hear the low frequencies well.