One week on, I'm beginning to love these headphones more now. I don't think I be returning them. I'm definitely getting used to their sound and appreciating that, despite them definitely not having a neutral or honest representation of the sounds given to them, they do allow one to enjoy a vast array of music in a very vivid way, which I can be nothing but pleased about.
I must add that I recently bought a cheap Bravo Audio Ocean tube amp. This was my first foray into tubes and was purchased especially to drive a used vintage pair of AKG K240 DFs (600 ohms) that I received just days before the HifiMans. Well, as it turned out, this little blue bundle is amazing and drives all my cans beautifully. I swapped the stock valve for a used Mullard from eBay and the difference was surprising to say the least. Aside from it bringing out the bottom end and filling the mids out on my AKGs (intended purpose), I found that they really tamed down that 'tizziness' at the very top end on the HE-400s. This was my single biggest issue with these headphones and I am over the moon with this pairing with the little valve amp! This very match stopped me from returning them. I just thought people might like to know that, in case they fancied a relatively low cost tip-toe into valve amplification..http://bravoaudio.com/Bravo%20Ocean.html