Ray J Wants Another Piece of Kim K

Ray J thinks it's a fabulous idea for Vivid Entertainment to sell the rights to "Kim K Superstar" ... so long as he gets a big piece of the action.

TMZ broke the story ... an undisclosed private party has offered to buy all rights to the XXX flick from Vivid honcho Steve Hirsch -- which he told TMZ is worth at least $30 million. The buyer indicated he (though we're guessing it's a she) wanted to take the video off the market.

TMZ has obtained a letter from Ray J's lawyer to Hirsch, in which the attorney makes it clear ... Ray J has partial copyright ownership in the video and "any attempts to transfer the copyright outside of these parameters will result in filing a motion with the courts to seek an injunction of any sale until Ray J's rights are protected." Translation -- he wants some serious cash.

The letter also says the video has been a pain in the ass for Ray J: "... my client rarely has a conversation with industry professionals where the Tape has not been mentioned or questioned ... no amount of money can relieve him from this nightmare." The lawyer didn't mention how much money Ray J has already made from the video.