Neopixel LEDs reacting to music from Music Maker MP3 shield

I'm working on a project that involves some Neopixels reacting to music coming from an Music Maker MP3 shield.

Separately, each component works; audio playback via speakers and sound reactive lights via an electret microphone amplifier and code from this project I tweaked.

When I put them together (ie, when I add the code that updates the Neopixel lights to "while (musicPlayer.playingMusic)") the audio sputters and the neopixels flash red sporadically (I have the neopixels set to green and reaction to sound is based on brightness)

Have I bit off more than I can chew? Or is there something I'm missing

Thanks