have you been to this rotel forum:
http://www.htguide.com/forum/forumdisplay.php4?f=20
?
most the people here will say there's no difference at all between the two pre-amps
most the people on htguide will say that the difference one and the other is night and day.
IMO, I'd go for the RC1082/RB1092
RC1082 because it's newer, and the push button source switching is a great idea, I also think it has tone controls.
RB1092 because it's got a lot of power, it can run your 100's (and whatever future speaker you buy) 2.0 no problem.
the RB1080 has some fuse issues (which pretty much renders the 12v trigger useless, rotel has said they fixed this issue already - you can distinguish the new units by the 4 pairs of speaker binding posts, the old one has 2 pairs, though there are those with 4 pairs that still have the fuse problem)
the RC1070 is pretty old, though it's all I can afford myself.