Well, it's slightly better at 100ohms with tinfoil shielding, but not better enough. Back to an external phono stage for me, I give up.

As a side note, WM's sheet of ERS (the magic dishcloth with claimed RFI-reduction properties) doesn't appear to do anything at all, at least not in this application. I've tried it both inside and outside the case, with precisely zero discernible effect. Sorry guys, I think the claims for this product need to be taken with a large pinch of salt; whatever it does (if anything) it certainly doesn't make any audible difference to a very audible RFI problem.

-- Ian