Been a while since I have posted on this thread. Things have come and gone but I keep coming back to the KSC75 and basic Grados (SR80e). They share a commonality of midrange presentation, endless opportunity for modification, and a bang for the buck that far exceeds their selling price.
After a lot of playing around I have found, for myself – ymmv, that the drilling of the KSC75 cover plate stops at a pseudo clover leaf. Anything beyond that may alter, but for me, will not subjectively improve the sound. This configuration really optimizes the bass and even outs the overall tonal balance. Whereas I have found that my preference on PortaPro drivers is to leave the plate stock.
Lots of pad experimentation. Quarter mods, reverse quarter mods, Grado flats ('comfies”) on top of the stock Koss pads, Grado L-Cush on top of the stock Koss pads, Geekeria S-Cush replacements (which have a center hole) over the stock Koss pads. But the running config that has dominated is a set of Sennheiser HZP32 pads over the stock Koss pads. Until now.
GET THE YAXI PADS! End of. They are the solution. I got a set Friday and all other options are now obsolete. Immediately ordered more. I only regret that I don't like any of the colors other than black...except the Acid Purple – that they do not make for the Koss. HOWEVER...they now make a Grado pad, somewhat an S-Cush, stiffer but also softer. For now they are my goto pads on the SR80e.
The other mods to the SR80e...vented the drivers. Stock there are two vent holes. I opened up three more per driver. LF response dramatically improved. Damped the ear cups and the back of the drivers with adhesive backed felt. Replaced the headband with a padded sheepskin band from Amazon. Screw Grado for not putting a padded headband on the 60/80/125 headphones. Cheap bastards. But still, these relatively inexpensive changes fundamentally change the comfort and SQ. Makes me less and less curious about trying a set of RS2e or Hemps. I mean I'm still curious, just not $400 curious.
A note on the headband. The current generation PE headband with the angled bend is, imho, superior to the earlier curved headband. It doesn't require that I tape it in place to set the position of the drivers and it stays put on my cranium better. As to the PP band (I keep a set of KSC75 on a PP band in the office) I find using electrical tape across the top to keep the size exactly where I need it eliminates all hair pulling issues (not that there is much there to be pulled...).
I have somewhat abandoned the base KSC75 for the MassDrop KSC75x, solely for the color. I much prefer the black to the stock silver. I did just recently try the KSC75x for phone use. Connected to a lightning adapter into my iPhone7 the inline mic works surprisingly well. The only control on it is to connect/disconnect the call, and that is fine. I have no issue using the phone to control mute and volume.
What I REALLY want is to convert the KSC75 to mmcx so I can use more robust cables but I have not been willing to instigate the surgery. Doesn't seem like there are any practiced hands selling it as a service.