I picked up the 598's and ran them 24/7 for 3 days in the basement - playing "Flight of the Cosmic Hippo" on repeat. Figured that would help bring them around. To help with the clamp (out of the box they were more firmly grabbing me than my buddy's 2 year old 558's) I stretched them across my subwoofer (about 7 inches).
Picked up the Cayin HA-1A yesterday. Switched the Matrix Mini i into DAC mode (so the volume control is out of the circuit), plugged in the Cayin and the 598's. Switched the Cayin into triode mode (vs ultralinear), cued up some songs on iPeng and sat down last night around 7pm.
At 11pm I realized that is the first time I have ever worn headphones for that long without a break.
The velour pads will soften up in time, and this combo will be a great source of musical enjoyment no doubt. I imagine there are N many ways to secure better detail, or more bass, or whatever more expensive stuff bring to the table.
Factor I have spent about US$450 for the Matrix, the Senns and the Cayin (all used, but the Senns which were NIB) and I am quite happy. I could see another $100 being spent on some great tubes, and then sitting back and enjoying.
I will write up a more thorough review in time.