Mp3 audio in node.js with gain control

I'm trying to play some mp3 files in node.js. The thing is that I manage to play them one by one, or even, as I want in parallel. But what I also want is to be able to control the amplitude (gain) to be able to create a crossfade in the end. Could anyone help me understand what it is I need to do? (I want to use it in node-webkit so I need a solution that is node.js based with no external dependencies.)

This is what I've got so far:

var lame = require('lame'), Speaker = require('speaker'), fs = require('fs');
var audioOptions = {channels: 2, bitDepth: 16, sampleRate: 44100};
var decoder = lame.Decoder();


var stream = fs.createReadStream("music/ge.mp3", audioOptions).pipe(decoder).on("format", function (format) {
  this.pipe(new Speaker(format))
}).on("data", function (data) {
  console.log(data)
})