Soundtraxx used to make a nice Alco decoder. I have three already, and they sound just like the Alco sound. I put one in an RS1, and the other two in a couple FAs. I still need one more. Does Soundtraxx still make the Alco sound decoders, or does anyone else make a good Alco decoder.
Soundtraxx still makes DSDs and DSXs sound decoders, with a generic Alco sound.
You might want to check ESU’s Loksound decoders, which are available with a variety of Alco engines (539, 244, 251…) with differentiated sounds, and excellent motor control.