Cobbler, you made me curious. A bass-playing friend of mine had for a little while the RS-180's (one grade below the RS-220) , but he returned them: he found the latency unbearable, and that one even had some sort of compressor (Automatic Volume Compensation, or something). So when he picked a string, he could not hear the attack, and the tone 'faded in'. He contacted Sennheiser support, and had a response along the lines: yeah, if you want that Jazz-bass slap or Telecaster-quack you should go for a wired headphone. The wireless phones are for listening to mastered music, not solo instruments.
Since at that time I was thinking of buying the RS-220 I compared specs, and only found that with the RS-220 Sennheiser did not mention the AVC, but there was also no specification for the latency (in milli-seconds, for example). I then dismissed the idea. You have me rethinking this!
Can somebody else confirm that these RS-220 are gooed headphones, also for practicing? I hate that wire when playing guitar.
Oh, and when you say practicing around the house, do you also have a wireless guitar set (Line6, f.e.)