In case anyone is interested, I currently use the ER-4P but equalized into the ER-4S on my PC. With a link I found on Rin Choi's blog by a poster named Carrot in the comments. http://rinchoi.blogspot.com/2012/08/p2b-adapter-for-etymotic-research-er-4p.html If anyone is interested, that's...

Grr, I signed up to ask about this. I need one of these adapters to turn my ER-4P into the ER-4S. Guess I'll get one from ebay, anyone bought theirs from ebay for around the same price?