Thanks for the reply. I actually own Dusty's D-100 monoblocks and they're great, so my first thought was the CIAudio headphone amp.
The problem is that I'm in Australia and, having discussed it with Dusty, I would also need to get the separate power supply to meet Australia's electrical standard. With delivery and customs duty, the CIAudio option would end up around A$900, which seems overkill for a A$300 pair of cans. I can get the rega locally for A$390, which is well under half the price of the CIAudio.
Are there any other options apart from the Rega? Locally, I know I can get the Musical Fidelity X-Cans V3 (A$550), Talisman T-31H (A$599) or Creek OBH-21 (A$425).
I can't actually audition any of the options as they would need to be ordered in, but would any have better synergy with the 595s than the Rega? The reason I find it the most attractive is that it is the cheapest and I don't really do a lot of headphone listening, which is not to say that I don't want the little I do to not be good!