Yeah true! In fact the PX 210 I think since mid/late last year has been discontinued already (although Amazon still has lots of it). If it has the same driver than those then much better since there's no need to upgrade for me.
As for my device, I'm using a Galaxy phone w/c has an A2DP 2.1 Bluetooth. Probably not really hissing and could be that I'm just being nitpicky. Either way I don't have plans to get that bluetooth dongle or whatever from Sennheiser since I heard there's not much difference in sound quality