Both of those capacitors are used in other ways than as bypass ones, i.e., it's not that the capacitors in themselves are a downgrade in quality (though of course there are better - and more expensive - ones). Smaller value caps are faster in output than larger value ones and therefore their information reaches the speaker drivers sooner than that of the larger value capacitors. They may indeed perhaps extend the frequency response of the unit they're used in (or just add "air") but at the cost of smearing the timing. People are more or less sensitive to timing issues so, as usual, it becomes a personal preference.
That is interesting! If only there were one simple formula/components to make that perfect sound!
I've went down that road some years ago with trying different interconnects, speaker, and USB cables, and noticed changes in quality for better and worse! I also know that from my own personal listening experience, that it comes down to the components that are in the complete system! I don't think that one could hear much difference in a cheaply built system versus a well designed and of higher quality system! "Not saying that less money versus more money is worse" but rather design and quality!!! But usually, you get what you pay for!
Now a few questions on the bypass caps: Suppose one would take the cheaper Bennic, Solen, or Parts Express film brand caps and use them in the passive crossovers with high quality built drivers, will one notice a difference in sound quality versus using Duelund capacitors?
How about if one likes the sound of bypass caps, should one choose Polypropylene/Teflon, Aluminum film, copper foil, etc.??? And will these different types make enough difference to hear and say that is the magic cap?
How about the Duelund CAST-Cu-Ag Hybrid Loudspeaker Capacitor 100VDC. Technical specifications (according to manufacturer): "Inside the Duelund CAST hybrid silver-copper capacitor there are two capacitors: a main copper foil capacitor that is bypassed by a small silver capacitor. They are both potted together. The lead-outs are intertwined from both the pure copper foil capacitor & the pure silver bypass capacitor hidden within the CAST potting. Premium VSF-CAST speaker capacitor; pure copper / silver; handmade in Denmark."
BTW, I looked up distributors in the USA for Duelund, and can you believe that they list Parts Connexion, who by the way is IN Canada, a USA distributor?
Now if you are lucky enough to have low valued caps in your tweeter circuit, you may be able to upgrade to these Duelund caps for maybe under $2,000.00 for a 2nd order filter! They better be able to sing me lullabies each night before bed-time!