DC/DCC sound. That is awesome!!
Every W/sound decoder these days is dual DC/DCC capable Jerome. The disadvantage with running them using DC is that when you bring them to a stop, so the sound stops as well (and any lights). To get a W/sound loco to get moving again requires advancing the throttle to about 6 volts input to the track. That gets the lights on and the startup sound sequence going. Increasing the V input gets it moving. It is also the reason, consisting DC only locos and DCC/sound locos is not possible, or advisable.
On the other hand, as I now recall you have mostly silent DC/DCC decoders in your locos, I'm not sure whether they will consist on DC either, they will on DCC though.
I'm not 'up' on Stewart, but from what I've gleaned, they may have had different brands of decoders at different times. BLI for a while made a 'Blueline' sub brand that had a DC/sound decoder in it, You had to piggy back a silent DCC decoder onto it, if you wanted to run it that way.