I'm building a simple headphone rig as a gift for a friend who's going through a bad spell and could use a care package. He's a guitarist and has a good ear, so it needs to be reasonable quality, but I don't want to break my bank. I've scrounged up a pair of Senn 555s and am looking for an...

Currently have only iMac and DAC1. Optical miniplug to Toslink cable = $30. HagUSB + bog standard interconnect = $160. Can afford to go either way, but don't want to waste money if there really isn't going to be much difference. So, to paraphrase I guess, how bad is toslink really?