Posts Affecting Multiple Series

[LittleNellie'sDad]

Question: I recently did a custom upgrade to my sound system for which I did a lot of research and waded through a lot of information. I'd like to write a post helping others who are in the same situation. While I was upgrading my 230i coupe, what I know applies to all coupes/sedans up through the 4 series, also X1s-X6s (all have the Harmon Kardon upgrade option). What would be the best way to post so that all these vehicles are covered?

Thanks!