Massimo - The early 3.5 tweeter feed used a 6.5uF feed cap. It was tweaked in 1987 to 8uF, which is what you want. Only buy now if you need it. I will have a much better replacement soon.
The 3.5 mid and tweeter are front-burner projects. We are incorporating late-stage design elements into the 3.6 midrange platform - dual cone, advanced motor, to fit the CS3, 3.5 and 3.6. The 3.5 tweeter is obsolete and our replacement will also incorporate late-stage advancements to fit the CS2, 2.2, 3, 3.5, 3.6 and 5. Completion of midranges and tweeters is necessary to re-work the crossovers between them. For now, get your advice from Coherent Source Service.
The ScanSpeak 10F8424 is not robust enough; it will burn out. SS’s recommendation for drop-in is 12W/8524G00. CSS may have that driver or another of their choice.
Tom