I think 6% is not too too bad as a fee for spending money. What I do not really understand from your question is that you seem to expect to create this "travel money card" in Amsterdam when you arrive. And how do you expect to pay for it? In other words, if you can pay a large amount in Amsterdam to buy a prepaid debit card (because that's apparently what it is), how come you cannot pay small amounts on a daily basis with the same payment method?
Anyway, these multi-currency cards do exist, I found for example the offer of Mastercard, offering to have a couple currencies on one card (the choice is limited, as you are going to Europe only British pounds and euros would help you) but the fees are quite high: 10USD to create it, 2GBP-2.5USD for ATM withdrawal, free payments and a fee on currency conversion (I am not sure I read well, but maybe up to 5,5%). And this offer is intended at US customers, it is sold only in Travelex stores and some banks there. On top of that, this kind of card is not always reloadable and you cannot get the money you did not spend back. So, even if it worked for you, the overall fee by mostly paying with this card and withdrawing a bit may reach 3-7% (<1% for creation, <1-5,5% for conversion, <1% for some withdrawal).
For the Netherlands, there is a comparison of different cards. For example, one of the cards, which offers mostly free transactions, seems to have a currency conversion rate about 3% lower than the market.
I would recommend you to look at this question that summarizes the most popular methods to manage money abroad. In particular, I believe your own debit/credit card would do. I do not know what Brazilian banks offer, but in Europe Mastercard and Visa are widespread, if you have such a card that is good. Make sure your bank offers low fees on ATM withdrawals or payments or try opening an account in a bank with better offers. But the cost of spending money is still high. Banks in my country often offer rates around 2-3% + base fee (1-3 euro) on most transactions abroad, plus the Visa/Mastercard conversion rate that takes about 1%.
So I let you read the answers to the other question and make your mind about which solution is the most convenient for you. Remember to carefully read the conversion fee and rate, the payment fee, ATM fee and creation fee.
