Backer Boxes & Backer "Channel"

[Zenon Marko]

Good morning/day/eve -

A couple of general questions on backer boxes:

1. Is it reasonable (or profoundly unwise) to consider building a single "backer channel" to house a row or recessed lights and speakers in a soffit, rather than individual boxes for each light and speaker?

2. What about a very large backer boxes, such as to hold a large ceiling cassette HVAC unit? (The unit I am considering requires an 18"x48" ceiling opening). I am considering this as a visually more aesthetic solution to the more common (in music studios, at least) but uglier wall-mount Pez-dispenser style.

Thank you for any advice, experience, humorous anecdotes.

Best regards