To that point... interestingly enough, I went home and fired up the Woo Audio WA7 and plugged in both the K545 and the K551 for S&Giggles and funny enough the 545 came out ahead in this one. Makes no sense but can't fight what I heard... 545 sounded full and smooth when just out of a portable it sounded harsh and hard. 551s sounded more emaciated than ever!! Go figure.
Too bad I'll never use that combo anywhere but home, which defeats the purpose of having a decent portable setup (she writes in bliss with HD800s and WA7 with Annie Lennox blazing "Waiting in Vain")
As far as which of the AKGs are technically superb, I'd say its an even playing field despite how I feel about the K545s. Though they have quite different SQs, I don't think AKG skimped on the 545, I just think they are a different flavor of the K5.. series in which they tried to incorporate we the listening public's wishes (more bass, fuller sound) but for me, that took too much away from what I loved about them in the first place.
Still not sure which to keep so I'll have to flip a coin. Tired of swapping back and forth - I just want to enjoy the music now!
Happy listening - I mean isn't that why we do this? :)