For many years I used inexpensive Phillips Fidelio X2HR; paid ~240 CAD and generally satisfied. Wanting to see if I can get better sound now that most of my music shifted to TIDAL. Sennheiser HD 660S was on sale (500 CAD, regular 640 CAD) so let's see is the brand worth the hype. I am using AUDIRVANA as front end app and Cambridge Audio DACMagic 200M, into which I plug headphones.
First impression: Good packaging and cables. Comfort also good - even if some reviews mention this could be a problem. And this is where positives end. To me most important feature is sound quality and this is clear downgrade from Fidelio. Murky with no clear distinction between high/lows. I gave it time as headphones need to be 'broken' - after 4 months no significant improvement. Also needs adapter to plug directly into Mac headphone port (Fidelio fits directly and had included 35 mm adapter for plug into DACMagic or standard HiFi Receiver)
Bottom line: Sennheiser is not worth the hype, at least not 660S model. There is reason why WHATHIFI does not recommend it. Go for Grado SR325X instead in this price range, WHATHIFI winners and still cheaper than 660S. Likely to try to sell them now