@kokakolia there are some huge differences between kitchens and hifi systems. In a kitchen the different storage units must fit and the doors must fit the storage units but other than that it's mostly about how it looks.
If you have a crossover and some speaker elements that fit you can't just change one of them. Even the box affects the sound and has to match the other parts. I know there are some good kits out there but the best solution seems to be a complete set with drivers and crossover and a box that may need assembly, like an Ikea chair. What you save money on is that the box may use simpler materials and not look pretty and of course the assembly.