Since you are using a stereo sample keyboard, plugging in both the L and R into a mono system will probably sound better than just L/R Mono, R alone or L alone. It should have a fuller sound with both channels wired. Try it all ways and let your ears be the judge. My experience has been that both the L and the R wired to a mono amp trumps the "L/R Mono" out alone.
[This message has been edited by petros (edited 03-20-2004).]