Zend certified PHP/Magento developer

Custom filter search problem

I am trying to add custom filter to layer navigation. Basically I didn’t have any problem with displaying it on navigation sidebar but collection filtering is now the problem.

I have filter which is NOT product attribute and that filter has two possible items.
Each item should be filtered by two product attributes.

E.g:
New collection item should filter by attribute1 AND attribute 2…

I overriden search_request.xml and added my new filter item but I am not sure what is the problem with collection filtering and returning total number of products ( count item of filter ).
I am using Amasty layered navigation which does some custom filtering but I am unable to find a place where collection filter conditions should be added.

Any help is appreciated.