In some old brochure scans of early models from Panasonic appears MAC, what's the meaning ...

See that ... It would be great to built some sticker

I can't say exactly why Matsush1ta in Japan called the RS-4300 a "MAC," but it was/is common for Japanese manufacturers to add names to products sold in Japan. There seems to be a fascination in Japan with catchy English words.

For example, some Japan-market National SW radios carried the nickname "Cougar," while others were called "Proceed." Some portable walkman-type players were called "Jump." I have an early (maybe the first) model National VHS camcorder, and it's named "MacLord." More recently, Victor (JVC) used the name "Slendy" in Japan for a boombox that elsewhere was simply known by its model number, RC-NX3. The Victor UX-A70MD three-piece, minidisc compo unit was called the "Lip-Lap" in Japan. Finally, one of my favorite mini's, the Toshiba RT-SW9, had the nickname "Sugar" in Japan.

The "MAC" in the Japanese ad you scanned may well stand for something, but I'm guessing it's just another cute English name (Hitachi used "Perdisco") given to a Japanese boombox.

Yeah, I saw "cougar" in most early radios from National, like RF's or RQ's. I tough it was an off-brand of National.