Items used:
ESU 58429 LokSound 5 21-MTC decoder with DCCSound 1st series X class sound
DCCSound Premium twin driver sugarcube speaker
The inside of the model is accessed by removing the coupler boxes and four screws under the chassis (one at each corner). There is a lighting wire connecting the body to chassis, so take appropriate care when removing the body.
Remove the supplied speaker enclosure from the model. Retain the screws as these will be used to mount eh new speaker.
The small DC jumper board is removed. Note its mounting orientation.
The decoder will need to be inserted onto the 21 pin plug the same way, i.e. upside down to normal NEM660 convention.
Position the speaker into place and attached it using the two small screws previously removed.
Reassemble the model by fitting the body, screws and couplers. Blu-tak can be used to keep the sanding lines away from catching on the chassis, the trickiest part of reassembly.