I feel blessed i came across this thread prior to purchasing this instument. This is straight up shocking. So to clarify these loose knobs are considered acceptable by DSI? I just read this post watched that video posted with the loose knobs and that is just plain crazy to say that's acceptable for an instrument so expensive. I was really looking forward to purchasing this instrument and has put me right off regardless of warranty.
The construction is no different than that of, say, a Sequential Prophet-600 from 30+ years ago; then as now, the potentiometers were soldered to the top-panel PCB but used no retaining nut to clamp the potentiometers to the metalwork. There are arguments both for and against this approach, though it's generally much easier to replace the top-panel PCB than to fix bent metalwork....
That said, the knobs themselves have a slimmer (rectangular) profile than those used 30 years ago, with a smaller diameter, so it's much more obvious when a shaft is slightly off center, compared to the OB-6, for example, which uses a different (SEM-style) knob with its square-ish profile.
I've got a Mopho SE of similar construction as that of the Prophet-6, with nary a wobbly knob in sight, for what it's worth.
If one was particularly concerned about this, I'd demo and visit a retailer which
stocks the Prophet-6, so that you can inspect the unit prior to payment.
While it may be the case that your expectations regarding build quality are higher due to the import / distribution price differential, it's
your money–and it's perfectly fair to question fit and finish. If there's a bad batch of PCBs, or of knobs / encoders, it's statistically likely that all units from the same manufacturing run would exhibit identical behavior.
If, on the other hand, not all units have the same issue, then any and all defective units could have their top-panel PCBs swapped out by the local service center.
DSI has generally been pretty responsive when it comes to manufacturing issues, which is part of the added value when buying their stuff, as opposed to, say, Korg or Behringer.