I like the tank engine sound in my Tamiya Leopard 2A6 and KV-85 tanks but decide to improve a sound quality.
In my KV-85 I simply exchange the original small Tamiya speaker to big Visaton 10 cm speaker with very good bass reproduction.
Tamiya Leopard 2A6 electronics have unfortunately small built in amplifier, so decide to use external amplifier supplied from 12V. This voltage is taken from step up converter (7.2V to 12V) . I exchanged the speaker also and drilled some holes in tank upper hull (over the speaker, later covered by grid imitation- 1,2,3).
Now both tanks sounding much better.