Capacitor update - how do they sound like?

IMO, you'll get more reliable results by auditioning different speakers.

These should be plenty bright-I have some and even with the presence and brilliance knobs less than halfway up there is lots of treble.Determine that the tweeters are working. If you can't hear them, make sure they're not blown. if they are still good, clean the L-pads with a good quality solvent like De-oxit (you will need to remove the crossovers from the cabinet- don't just spray stuff "at" the pots) and rotate the pots several times to disperse the cleaner. if that doesn't help, the L-pads may be toast- replace them.

To be clean in color and background, change the resistors from the sand white type to one such as MILLS Non-Inductive Wire Wound Resistors. Changing magnetic core inductors to air core inductors (will create more loss due to more turn so have to reduce resistors in same path or increase resistors in different path for loss equalization). You can also replace electrolytic to film cap. Different manufacture caps will result different characters in sound. All three will improve your problems.

Thanks sincerely to those words of wisdom...
I will definitely consider all the advices!
Please keep them coming, if someone has more to add...