Dapol's current HST range of models are great candidates for taking DCC sound..
Motor car with MX649N direct plugin. Note the screw mounts that held the factory socket board in have been chopped down, so it floats lose, but slightly
lower. Insulate carefully, but it is fine for it to float a little. SugarCube7 speaker at the back.
Also added a cab light and crew to this one... quite an easy extra...
Dummy car has much more room, but a stay-alive is useful here since it is so light - Zimo SPEIKOMP kit with 330uF stay-alive added... a couple of tantalums
would also be a good option. MX648F used with SugarCube9 speaker.