I love the Sennheiser sound too! I have a pair of HD-600s that must be close to 15 years old and have many thousands of hours on them. Hopefully there will be a Sennheiser wireless model that betters the RS 220 in the future.
See my post right above yours. No fixes that I'm aware of. 1. My batteries started to wear out in less than a year. That is too short a time. As they wore down, performance suffered (i.e. more and longer dropouts). I filled in a warranty claim with Sennheiser and am now waiting to hear back from them. (Also, I do not see replacement batteries for sale on their website. I'm sure you can get them elsewhere, but it seems strange given the short life span.) [Edit: I...
I really liked the RS 220 when I got them in Feb 2012. I had very few issues with dropouts except when I wore them while using my laptop. However, for the last few months I have been getting less and less charge time from them. Now, they will not hold a charge at all. As the battery wore down, they have had more and more dropouts too. I'm going to try to get a replacement battery, but I would no longer recommend these headphones to anyone. Too problematic.
I only spent ten minutes with them. They had an excellent seal and a very balanced sound. Unsurprisingly, they sound and look a lot like my LCD 2s. Imagine a pair of LCD 2s with the leather headband and wooden cups. They are not noticeably heavier than the 2s despite the cups. The bass pressure inside the cups was very strong (more than my HD-25 II); I need to spend more time with them to decide if it is a bit too much for my taste.
The benchmark headphone amp is excellent. It measures beyond reproach. Some find it a bit bright or clinical, but I don't agree. I sometimes prefer a more relaxed tube sound with headphones, but also enjoy the DAC-1's headphone amp and listen to it frequently.