Hi Joey, the app was recently updated to make iOS 7 the minimum supported OS version because that's now the minimum version allowed for a new iTunes store submission.
That said, before I updated my last remaining iOS 6 device to iOS 8, I did install PitchLab via iTunes and it actually downloaded the last iOS 6 compatible version so I'm surprised you can't install the app at all on iOS 6.
Can you please email pitchlabapp@gmail.com to discus the issue in more detail?