See post 2573 on this page. Look at part #10: Dust cover. Some have found removing this dust cover from the front of the driver provides more treble. I removed it and held it up to light. It is very thin and loosely woven. Some have removed it and noticed improved treble. I did not hear a difference, but I a deaf above 12k Hz. People with intact hearing in the higher registers may hear a difference where I did not.
I'm not sure what you are referring to as bass ports covered with foam. Where is the foam?
The bass tuning port is at the bottom of the cups and covered with a slightly denser fabric (part # 17: damper) compared to the thin dust cover. I removed it and placed electrical tape over all 4 slits. I slowly pulled the tape away exposing first only 1 slit, then 2, etc. until all 4 were open. Some have found significant increase in bass as more slits are opened. I did not notice a significant increase in bass when fully open; only a minimal change to my ears and I can hear down to 20 Hz.
FWIW: There is a very small hole on the front/ear side of the baffle. You can stick a paperclip through it and see where it comes out of the driver on the back side. This, I assume, allows pressure equalization on either side of the baffle; in other words, the pressure is the same inside the cup chamber as outside. You can experiment with fully open vs partially covered with tape vs fully covered with tape to see what effect, if any, is produced.
Let us know what you find as you continue your mods.
Vent tuning has the greatest effect when the white felt is removed. If that mod has not been made the ft dominates the damping of the bass. If the felt is off the port is the main damping mechanism.