I must be missimg something,, as Dave mentioned, your connections are coming from the output jacks of the keyboards to a passive volume pedal that acts as a "pot", then continues to the amp.. There is no difference then if the keyboards are connected to the amp..All the keyboards have a nominal impedance that amps[and volume pedals] can handle..We are making more out of this then we need too. As Dave said we 've been doing this for years..