Okay, getting the ORs in a sumifs is not really supported (or at least I don't see an obvious solution). This brings us to SUMPRODUCT
=SUMPRODUCT(--(C2:C300="AppName"),(LEFT(A2:A300,2)="PC")+(LEFT(A2:A300,2)="WC"),NOT(ISERR((FIND("XP",K2:K300))))+NOT(ISERR((FIND("7",K2:K300)))),--(L2:L300<>"test"))
I was also tempted to use DCOUNT, but you said you did not want to use filtering. Not sure if that fits in your definition of DCOUNT or not.