Just the 300Bs have a slightly thicker sound which I feel the HD800s need. Overall I do think the PX4 are much more awesome than the EML 300Bs I'm running. The KRs are harmonically rich, very clear, extremely fast, and extended and explosive bass. The PX4s sound great with HP1000s and LCD2s. kiertijai, as he mentioned above, obviously prefers the midrange voodoo of the WE 300Bs with his LCD2s. It really comes down to personal preference.
The PX4s I brought were Chinese made Sophias. They sound like crap compared to the KRs (which were currently not available a few months ago - supposedly because they shut down their factory during summer because of lack of A/C.) The Chinese Sophia PX4s have the clarity and speed, but lack the bass extension of richness of the KRs.
Edited by purrin - 10/13/11 at 5:28pm