Thanks for the PM.
1. I have changed your admin backend template to the default. You can turn it back on.
Look at the two screenshots from your site backend. Will try to explain below :
1. Your extrafields are all textfields. you should have used drop-down selection for your extra-fields, that would have given you dropdown option in the search param.
2. You have used text field and they can be used for range search (best done with numbers / quantities).
3. You can either update the extra-field values for all your articles and extra field values.
or you can try this :
Search box be set to : textbox
use JA-range for your search parameter and add the options in each line to reflect as drop down.
Hope you got the idea.
Arvind