The filter you show is a 6 db lowpassfilter with a impedance correction network. The L is the lowpassfilter. The RC is for impedance correction network. Other value will change the sound but if the builder done his homework right the value's are right. Why whould you change the parts?
If you change the value from 7.3 uf to 6.8 uf as you did, the crossover frequentie of the woofer goes down with 700 Hz ( asuming 8 ohm woofer). So this will sound different because there will be a 700Hz hole between woofer and tweeter.
How u calculate the Frequency? still using F=1/2piRC???[/quote]
Yes.
The impedance correction network ( CR) has a crossover frequentie of 2300 Hz. Below 2300 Hz the 3.3 ohm has no influence but above 2300Hz it lowers the impendance of the woofer.