Originally Posted by 3Cforme

So it's not just me who has become a little disenchanted with ITA Matrix.

It is still my go-to.

If the OP has specific questions about Advanced Routing Codes he should post them. There's a vast base of FT experience with Matrix.

Otherwise I offer this as a template for Matrix searches:

All DL-coded flights
Fixed departure
variable return +/-2 days
no change of airports (no LGA-JFK nonsense)
max 1-stop each way

...