i think the beyer and sonosax share the same case, but that's it
as for the beyer/psp3 connection, check doug's thoughts here:
http://www.oade.com/cgi-bin/miva?showmsg.mv+message=1734summed up:
>>So, you can build a design around a
chip, like the AD SSM2017 ( Beyer MV100 & Aeta PSP3 ) and you get a
certain sound quality. You can add features to it, like M-S
decoding, a rugged well designed case, interesting ergonomics, etc.
and get a package like the Aeta, that sells for more than the Beyer
for a good reason. Yes, they sound very much the same, but the
feature set is very different. <<