The EU taxdriver doesn't provide a default for displaying a pricePlusTax, as long as a user isn't logged in and already has a shipping address in his cart.

All the published item prices therefore normally are defaulted to net prices.

This it wrong and, at least in Germany, it is not allowed. If you sell to everyone, you have to publish endprices.

I could overcome this by a price macro to use for visitors but it would be better to have a default pricePlusTax based upon the admin's or another preconfigurable address and/or only the taxgroup for the item.

I think, dutch colleagues will have had the same problem.

Can someone advise me in detail about solving this problem?

Ik zou je erg dankbaar zijn!