All measurements from various measurement rigs say there is a 5kHz peak though and the sound becomes less 'edgy' with the filter.
Using different foam than the one tested isn't essentially the same. I tested various types of foam and densities (have plots in the article) and while all changed the amount of upper bass/lower mids they did so with different effect.
I don't recommend to use sinewaves and ears as a measurement replacement.
The foam discs are sold separately or you can buy Superlux foam discs.
No need to buy the pads at all even though they include the foam discs.
The effect the AKG foam discs have are described in my
HD650 article.