I wouldn't recommend using one of those rigid 1/4" to 1/8" adapters. It puts a lot of strain on the HP jack, which is probably just attached to the circuit board. You would be better off using a Grado adapter (good quality and reasonably-priced), or making your own adapter cable with a Neutrik line socket and plug. If you always use the 580s in this rig, why not just re-terminate the cable with a good quality 1/8" plug (e.g. Viablue, Switchcraft or Neutrik)?
Sennheiser also sells a version of the cable with a 1/8" jack. Under $40, IIRC.