I’m still not sure i’m getting it right.
You want to filter items with category and condition?
As i see you have already done categories filter.
So why can’t you just add another variable and put in into your query?
I mean something like this:
$cond = $_GET['cond'];
$SQL_GetEquipment = "SELECT * FROM `new_equip` WHERE (`condition`='$cond') $SQLCat $Limit";
PS: Are you store categories data in a single field? That’s very bad practice. You should use one-to-many relation. Learn about it here.