Well there you go.
Per Chris' prompting in the sputtering DSP33 thread, I upped the depth from +0.5 to +1.0 then did the width up and down changes while listening to something loud and bassy on MTV. Result; a subtle but repeatably detectable change as the width scale hit 0.9/1.0. Sounded better on the widest setting with the bass clearer and more precise, I guess becuase it is being handled by the DSP5000 (set to large) rather than the DSP5000C centre (set to small).
Over to the rest of you to experiment further.