So I picked up a pair of KSC75s at Radioshack this morning for $12.49.
Incredible value. I owned a pair of SportaPros a few years back for ~$20 and loved the full, rich sound. They broke. I then picked up a pair of Koss KTX Pro Titanium 'phones at Radioshack, and those have held me over for a couple of years. Super comfortable, very impressed with them, until I started hearing a buzzing in the left 'phone at low frequencies. I considered sending them back to Koss for a replacement, but then realized that shipping + their fees would = a new pair of KSC75s. Saw that they were on clearance at Radioshack for $12.49, and here we are.
Impressions: The KSC75s seem to lack the elite bass provided by the SportaPros, but the 75s seem more well suited to other genres of music. For example, I'm astonished to hear how well they handle classical music. The sound quality is brighter and crisper than my Sennheiser HD555s! They do lack the warmth and "presence" of the 555s, but for $12.49 ... wow. I think I might pick up a pair of SportaPros for running and the occasional bit of bass-heavy pop music, but ... oh, and for what it's worth, all except the SportaPros were powered by an Onkyo TX-DS595 receiver.