Hi!
Monster M-1000i are very good for the money (especially used). I didn't find nothing that betters them for the price!
But I'm not sure about the combination Marantz-Monster. In my opinion, based on listening tests with various Marantz and Philips Cd players, they mate very good with Van den Hull cables (D 102mkIII comes to mind). I rate the M1000i higher (and they deserve a much better front end) then the Hull's but it's not the most synergistic combination with Marantz/Philips.
So with Marantz CD players my vote goes to Van den Hull.
Best regards!