Graham,
I'm sure that if you strip away all the effects from any Korg sound you'll be sadly disapointed. The depend on the processing to get that great sound, so if you use a sound dry (like their GM map) it's awful!
Roland gives you reverb, chorus & delay on the sounds to enhance the playability - NOT to create the tonality. A little reverb or delay goes a long way to add sizzle to a sound.