I have two 10 year old Kato HO locomotives which reflect the then state of the art in terms of DCC sound. The main limitation, in my opinion, was the beautifully detailed but solid Kato shell  restricted the sound escaping to reach our ears.  Actually, there were several members of our club  with similar locos which share these feelings. 

One of my locomotives is a GE C44-9W in which I had installed the older Tsunami specifically designed for the Katos' unique light tunnels and motor feeds. As good as it was at the time, the DSM8 could not overcome the very restricted sound pathway down through the frame (this loco did not have the fuel tank mounting location). Hmm. What to do?

I purchased two Tsunami 2 decoders and several SSS Ufit speakers which have become my go to speaker for hoods. The frame's rear weight had already been machined to accommodate the DSM8 so that was no problem. I looked at the rear of the GE and discovered the "bat wings" were easy to remove. Then I searched for etched metal parts which would replace the molded solid plastic part on the Kato. Detail Associates has a GE grill set which are made for the Athearn version. But for not a lot of money, I thought, why not? Let's see how they fit thee Kato.  They arrived and fit nicely.

With the bat wing removed, I drilled 6 holes in the grating area keeping away from the lip which is the return back to the shell. I then used a small Dremel cutting blade to join the holes and remove the side pieces leaving the center most portion in place. I uses my files to dress up the cuts while leaving a very narrow mounting lip all around.

There are upper and lower pieces of the grill and I took the photo before I installed the upper piece. I used thin CA to bond the pieces to the frame and each other.

The top of the shell beneath the radiator openings also required modification so the speaker could be mounted flush and project the sound up through the etched grills.  Again, pilot holes and Dremel cuts.

Obviously the light channels had been jettisoned years ago for speaker clearance, so all I had to do was use some small diameter shrink tube as conduit for the new surface mount LEDs rear lights and speaker connections. I mounted the speaker flush with he top of the shell just beneath the bottom of the upgraded radiators. I used canopy glue for the main adhesive after a few CA tacks to hold it in position.

The sound test was amazing even with everything at factory standard levels. Equalizer tweaking is next. Basic weathering is an ink wash.

The Kato SD90 was easier as I just drilled out the solid fans and replaced them with molded fans with open grills and separate fan blades from Precision. Drill the pilot hole and let the Dremel do the rest till the new fans slip in. Add a wee bit of CA and paint. Same amazing sound improvement even before the equalizer tuning.

A final tip. As the original Tsunamis had front and rear LED headlights integral to the board, the simple solution is to replicate this on the new PNP style decoder. I marked the frame top where the original light met the front light channels. I used a 3mm diameter warm white LED and trimmed the legs to give me this projection. I soldered the common to the decoder and it held the LED in position. I then used a small piece of 30 gauge wire and 1K resistor to connect the common side to the LED's trimmed common leg. Let there be light.

I will supplement this post with a brief video demonstrating the sounds.