Thanks again for all the replies. I finally finished the schematic of the input section and crossover, it's attached to this post. I studied it a bit and now have a rough understanding of how it works, but there are some things i am unsure about.
Starting with the input, there is an differential amp which converts the balanced input to a single-ended signal. However, this stage has some gain, 2.9 for the inverting input and 3.3 for the non-inverting input. This unbalance will introduce some dc offset, but i guess this doesn't matter since the output is coupled via C26? Just curious why it is not designed with unity-gain? Also, what's the purpose of the capacitors C1 and C2, are those added for stability?
Then there is the volume pot after which the signal is fed to the filters. I think both of them are 2nd order butterworth types.
What's the purpose of the R5, R6 and C3 network? Is this just a voltage divider or a low-pass or both? After buffering it is fed to the low-pass, but shouldn't R7 and R8 be equal?
Can someone point me to a source where it is explained how I can calculate the cutoff of the filters, I only found stuff for designing filters and don't understand how I can reverse this to get the cutoffs.
Edit: corrected a typo in the schematic.