Electronic filters divide the frequency before the output and are not affected by the impedance of the speaker. ( this can only be tested at the source) Passive, inline crossovers take a full range signal from the amplifier and use physical capacitors or coils and their respective values are determined, precisely by the impedance of the speakers at the end of those speaker leads. If you use 4 ohm speakers on an inline passive (mechanical) crossover that is designed for 2 ohm speakers, you will end up with either frequencies that are too low going to and damaging the tweeter or a big hole in the frequencies played due to the midbass crossing over lower than it should and the tweeter crossing over to high. If I was sure that they are crossed electronically, any set, 2 or 4 ohm would suffice and only the volume would be impacted.
"We already know that the blogpost guy used the coaxial Alpines without issue, and the youtube guy recommends the Alpine S-S69C which appear also be rated at 4 ohm."
Again, what we don't know, ultimately, is if the are passive or electronic. Any speaker with the same configuration will act the same, not unique to Alpine. the impedance is a factor now and needs to be observed since we are erroring on the side of caution and assuming that the leads are filtered with passive filters. Since we are not going to test further to determine the type of filtering, we need to assume the wires use passive filters.
Here is something to chew on while I look for speakers that will work.
"We already know that the blogpost guy used the coaxial Alpines without issue, and the youtube guy recommends the Alpine S-S69C which appear also be rated at 4 ohm."
Again, what we don't know, ultimately, is if the are passive or electronic. Any speaker with the same configuration will act the same, not unique to Alpine. the impedance is a factor now and needs to be observed since we are erroring on the side of caution and assuming that the leads are filtered with passive filters. Since we are not going to test further to determine the type of filtering, we need to assume the wires use passive filters.
Here is something to chew on while I look for speakers that will work.
What Happens If I Use A Different Impedance Speaker On A Crossover? - Sound Certified
Using a different impedance speaker on a crossover can affect sound quality. Learn about the importance of speaker Ohms and crossover frequency in this guide.
soundcertified.com