If the electrolytic capacitors are the originals you should consider replacing all of them - it is not too expensive, and you have an amplifier that should last for more 20 years if you use high temperature types.
Be sure that your preamp can drive the KSA250 and remember that it must be switched on at less one hour before listening - sound from a cold unit is quite sterile.
However there are some good news - the best sound I ever heard from a pair of Sonus Faber Extrema was when they were driven by a KSA250 that has been playing for several hours, although the ARC Classic 150s were also very good.
Be sure that your preamp can drive the KSA250 and remember that it must be switched on at less one hour before listening - sound from a cold unit is quite sterile.
However there are some good news - the best sound I ever heard from a pair of Sonus Faber Extrema was when they were driven by a KSA250 that has been playing for several hours, although the ARC Classic 150s were also very good.