portapro. Not as sparkly as the ksc75s (non titanium coated driver in the pp) but from what i understand it is the same as the ksc35s which are highly regarded as better than the 75 by some. I just got a pair yesterday and haven't burned them in completely but they are in some sense more refined and less awe inspiring upon very initial listens compared to the 75s but overall i'm enjoying the sonic balance better with these. You can however clip the 75s, or any of the 60ohm koss drivers for that matter, into the headband. I might put my 75s in the headband and use the pp drivers for a closed can transplant as these change very little when closed. Also, i prefer the headband design which i find to be brilliant and far cooler than the px series that awkardly collapses on itself. Oh and a lifetime of replacement for just $6 and these have been around unchanged for over 20 years.
Basically, the pp is a headbanded, cooler (imho because i like the retro styling), better styled, more durable (no clips coming off) and better balanced and refined ksc75. Also, i personally prefer the headband design, included case and warranty over the px series and i find these more comfortable as they sit on the head lighter than the pxs