Cardas Audio developed a Headphone Interconnect cable called the Cardas HPI Mini to Female 1/4 Inch Adapter cable.
This HPI cable is thin and flexible and is terminated with 1/8" stereo plugs on each end.
It can link portable players to outboard amps, like the high quality iQube portable Amp.
Available in 6", 12" lengths with Right Angled 3.5mm Plugs or 18" and 40" with Straight 3.5mm Plugs.
An Adapter version is also available called the HPI-A in 6" length.
Outside Diameter: 0.127"
Dielectric Type: Teflon, Cotton
Cable AWG: 20.5
Shield Type: Single
Conductor Type: 3 Conductor, Golden Ratio, Constant Q, Crossfield, Pure Copper Litz