It's been pretty busy 'round here, but unfortunately because of the day job rather than the layout. But you didn't come here to hear about that - we all have #adulting challenges that get in the way from time to time. So given that your time is likely as limited as mine these days, I'll get right to it . . .
The Atlas S-2 comes with an OEM Loksound Select decoder. It runs great as-is, but I've discovered that adding a "keep alive" capacitor provides some nice peace of mind that the sound is never going to cut out nor is the engine going to do any herky-jerky and ruin the effect we're after on our railroads.
Fortunately, installing the ESU version of the "keep alive" (called a "PowerPack") is relatively straightforward. You only have to get over your fear of soldering - on really tiny soldering pads...
The first thing you do is remove the decoder from the motherboard. Just carefully wiggle/pry it off.
MY biggest challenge was actually being absolutely certain I was soldering to the right pads. The instructions help . . .