How much does a Zobel network and its components affect the sound of speakers?

Regardless of amplification, my Merlin Audio MMI monitors have always sounded bettter using the Merlin RC Master (Zobel) Networks consisting of a Dueland capacitor and a Caddock resistor in series bringing the tweeter terminals. I've heard that some have replaced the networks using Jupiter capacitors and Vishay resistors and different wires and spades. My question is, How much do the networks and their components and associated values affect the sound? At times my speakers, while having superb resolving ability, can occasionally sound edgy, particularly noticable with voices at higher volumes.