Holy cow, I also freaked out when I read your first post. It sounded like you meant the 8kx wasn’t compatible with the comfort kit.
People don’t usually use the word compatible when talking about something you wear where I am from.
Eg. Although I might start using the term when my wife asks me why the outfit she is wearing no longer fits
I will say it must not be compatible. 
as well. 
often say things like that about people whom really shouldn’t wear bicycle shorts.