I sold a pair a while back to a buddy who refinished them. You are right the original Marquis (PLC) were fitted with Dynaudio drivers. If I remember right it cost him about $300 a driver and they were very difficult to get.
However if you can fine a new set those speaker rock. They were one of the most revealing life like speaker I've ever heard. They were designed by the late great Mr. Dunlavy
Good luck.
Tony