Thanks, luo.
The topic you linked to didn't provide much info because that user was using custom fields, not taxonomies. The structure of how he set things up is also different from mine. So I couldn't get a clue after going through that ticket a couple of times.
The functionality I'm trying to achieve is common and can be done with jQuery + PHP (example demo: http://css-tricks.com/examples/DynamicDropdown/), I'm just unable to figure out how to implement it with WordPress taxonomies and Views parametric search.
Any other clues?