* New company to list on the Australian stock market * AMP announces A$200 million share buyback * Expensive separation costs to be funded by shareholders - UBS (Recasts with detail, background, analyst comment) SYDNEY, April 23 (Reuters) - Embattled Australian wealth manager AMP Ltd has ended protracted talks with Ares Management Corp to sell its asset management arm’s private markets business, instead on Friday announcing it will spin off and re-brand the unit. As part of the new plans, which come months after Ares had downgraded a proposal to purchase the whole company for $4.9 billion to a plan to take a majority stake in AMP Capital’s private business, AMP will kick-start a A$200 million ($154 million) share buyback.