A happy ending--I've trashed the Dual but found that the Ortofon OM20 it came with sounded better (better tracking, smoother treble) on my Rotel than the Ortofon Blue I'd just bought. I've sold the Blue and bought a new stylus for the OM20: net loss/gain, $0. I think this'll tide me over nicely till I can make a bigger investment in my analog front end.
Thanks for the help, folks.
Thanks for the help, folks.