I don't think so 20to20K. If your player says it can do the conversion, it can do the conversion, and will be able to sent your NTSC TV an NTSC signal from having converted a PAL disc (presuming that the PAL disc's Region Code is supported by your machine, or that if it isn't, you have a 'hack code' for the player to get around this).
I have the Yamaha S2500 Universal, and even though it's obviously not the same as your own player, I've just taken a look at its manual to see if I can help out here...
This might be key to the whole problem. My manual states (in the PAL/NTSC conversion section) that "
In Progressive mode, the output signals from the VIDEO and S-VIDEO jacks are the same as the format of the disc you play." It's weird I know, since who cares what is coming out of the VIDEO or S-VIDEO jacks when in Progressive mode given that you'd be using the COMPONENT jacks, but it just might be that if you try a component cable (if you dont have one, use three of the four ends of two regular audio leads), you'll be sorted...
Fingers crossed!
Regards
EDIT: In fact, I'd recommend getting a component cable anyway. Unlike from Component to HDMI, which you may or may not notice any difference, you almost certainly will notice an improved picure quality from Composite to Component.