Dave, perhaps I can make it more clear.  I work a lot of d x and prefer 
listening to the d x station below his qrg so as to be on the  low side of 
his signal because most pile ups work above his frequency and this puts less 
qrm for me just in case the pile gets close to his signal.  On my 590 I have 
a choice of c w or c w r so  I can listen to either sideband so perhaps that 
is why you have a choice.  It's not a different mode just which side of him 
you chose to listen.  Probably I have made it clear as mud hi hi. I could be 
way out in left field though.  73

ED K7UC