Sensible way to go actually, the HD558 is very relaxing, can be a nice change of pace from the comparatively exciting and aggressive HE400i. Similarly, my most used headphones are my cheapest, the Panasonic HTF-600-S, because it's relaxing to listen to, even though it definitely isn't the best I have. That and I don't have to worry about scratching the headphones when I'm working on arts and crafts stuff.
I didn't find the HD558 relaxing by any stretch due to the ever present sibilance. The uncomfortable (hard) ear pads and the the impractical 6.3-mm plug for computer and portable usage were marly minor annoyances in comparison.
The range succeeds the popular PX 100, PX 200 and HD 200 series models
Is this a quote from the official Sennheiser press release? If so, does that mean that the fabulous open PX100 series has come to an end? And are there any potential alternatives?