Yeah.... use 480i or get a new monitor.
I'm guessing you have a standard resolution arcade monitor correct?
Max resolution for that is 336x240.... in other words cps3 games are extended res games, not standard res. I'm not a monitor expert... you might be able to get standard res monitors to support extended resolutions or some of the newer standard res monitors might support extended res, but afaik they don't.
I wasn't offering a workaround in my last post, I was explaining that there isn't one. Sorry.