Monday has proved to be a busy day at The Hawthorns as the Baggies also struck a £6million deal with Fulham for Diomansy Kamara.
Albion supremo Peace always insisted there was no financial pressure to sell the club's star players - and managed to rake in over £11million for arguably the two best performers from last season's squad.
Peace said: "We have said all along we will only consider selling players like Diomansy and Jason if we receive head-turning offers and that the deals are in the club's best interests.
"We feel these offers mirror those criteria."
The news could trigger Birmingham, Fulham, Blackburn, Everton, Derby, Reading and Aston Villa into action as they have all been linked with Koumas since the season ended.
And Baggies boss Tony Mowbray, who has already recruited striker Craig Beattie from Celtic and defender Shelton Martis from Hibs, has lined up a move for Norwich's Youssef Safri as Koumas' replacement.