I have heard that the only difference between these two is that the PC155 has a detachable USB audio device adapter (which I don't need). However, the web site says that the PC155 has XL ear caps while it says nothing of the sort for the PC150. Further confusing the issue, XL ears caps implies circumaural to me (around the ear) while all info on the PC150 that I have found suggests that they are suppraaural (on the ear). From what I can tell from pictures (haven't seen them in person), the PC150 look like they have the same ear pads as the PC155, which strangely enough, do LOOK like they cover the entire ear. I also noticed that the color of the 2 units is different. Although this is minor, it suggests that the different packages are NOT based on the EXACT same hardware and perhaps other things could be different as well. Finally, the website mentions that the PC150 ears pads are interchangable, but I have not been able to find any place where you can by different ear pads.