Phil, long time no hear, 'no hear' being the operative phrase! Clear inner ears and sinuses are probably the greatest upgrade of all, don't you think? I mean what would you rather have, your hearing back, or a new component right now?
Please forward your findings on cap upgrades to the Def 4 tweeters in due course. It seems Sean at Zu is soon to offer choice of caps as upgrade options in future. As of present I'm investigating Duelund Cu VSF or CAST options. Would love your considered opinions.