State variable filter preamp

[garfo]

I have built everything and it is working.I had to put two 10k resistors in series with the output of each preamp because they were fighting each other when mixed in the middle position.Someone told me to do this and said that 10k resistors should work.It feels like I've lost a bit of the high end when I did so.
Is 10k enough, or should I increase the resistors value in order to get the most treble out of it?