Stereo Linkwitz-Riley crossover

The following code processes an incoming stereo-audio-signal and a prepared mono-sub-signal and calculates a crossover with 24dB for the top- and sub-output. The calculation of the coefficients can be found down below. Please have a look at my X/FBAPE-project at GitHub: https://www.github.com/xn--nding-jua/xfbape The coefficients can be calculated like this: