ronkent - Regarding your mod. Be aware that the 3.7 mod that Rob suggested applies to only some speakers, not all. There was a QC problem with FST that required Thiel to test and characterize all incoming 3.7 coaxes and apply padding resistors as needed to bring the amplitude to standard. There were also harmonic distortion problems, which were failed and rebuilt in-house. When reworking drivers, CSS would add the resistors directly to the input terminals, or as in this case specify where to put them in the crossover.
Later, the coaxes were built to proper spec and noted with black trim rings. The 3.7 has an octave-to-octave balance within ± 0.5dB. So, you don’t want to pad it down unless it is out of spec, which is possible.
Note also that the mod as described here (padding both mid and tweeter) would effectively raise the woofer level a couple of dB. Moving the speaker closer to a boundary wall should accomplish the same thing. Also, any perceived brightness could be caused by harmonic distortion rather than simple excess amplitude. In that case padding down would reduce the gross amount of distorted output, but not cure the cause.
Roxy54 - for the record, with the 1987 CS3.5 we converted from 60/40 solder to silver solder for all our speakers. Our choice was the aerospace standard Alpha SAC-305 which is 96.5% tin, 3% silver, and 0.5% copper. It is not only permanent, but is technically superior. The improvements are audible. It requires higher melting temperature, but achievable with a 140 watt soldering gun.