I believe it should be approved by a majourity of all owners not just the EC, but whether it legally needs to be is another matter.
What is it going to cost to obtain these 3 quotes and is it within the spending limits of the EC??
Also once the designs have been obtained they will need to be approved by a SR (75% in favour) as it is an improvement and you are more likely to obtain this if everyone was involved at the begining.