I’ve made some changes to the project to help you out. I’ve changed the low pass filters’ bandwidth to get a better result. I’ve also changed the bit rate to be configured globally, so that many values are calculated automatically, like bandwidth of some filters, the time window on visualizers etc.
The demux channels and the Bessel filters are still not matching completely with the channels that are being fed into the multiplexer, so try to check out those values and determine how you want to center the demux channels and what sort of bandwidth they should be. However, the first BER Analyzer seems to be giving reasonable results.