Hi possessed,
I can vouch for the phono stages sold by LifeStyle AV - I supplied them! 
Seriously though, I selected and tested the Vivanco phono stage in these kits using a Beogram 3000 and Beosystem 3500, so I can be confident that you will get a good result with your BG3000/BM3400 combination. The kit is intended to be a complete "plug and play" addition, with everything you need to add a Beogram to a B&O system with line level inputs and it can be left permanently connected to the mains if desired.
Best regards,
Steve.
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