Hi Crobo,
Coming into this late, but I have a suggestion. Of course it may be an amplification issue, but there is also a slight possibility that your Vertcial Tracking Angle (VTA) may be a little out. The arm on the RPM6 has adjustable VTA I believe. If it sounds a tad less toppy than in the shop, its possible that your VTA is adjusted a little tail down. Raising it may sort it out ... and of course cost you nowt. Of course it may not be the problem at all, in which case back to pondering phono amps

But its always worth trying something free before parting with the readies.
Good luck
Unc