I have the Fostex TH600. I used them at work for a bit with my Pan Am. First, they leak sound A LOT. This is not an office appropriate set of cans if you are working near other people. You will also have sound leaking into the headphones if you are in a noisy environment. This describes how I make my living so immediately these headphones are eliminated from me being a potential owner. The T50RP is definitely better if this is an important factor.
I am listening right now on my Oppo BDP-105 with the latest beta firmware, BDP10X-60-0808B. These are a surprisingly good match for the Oppo! Bass is HUGE with big impact. There is a ton of detail and very clear and articulate separation between all instrumentation. The sound stage is pretty good, but not quite as good as the HD800 I auditioned several weeks ago. The Oppo is driving the TH600 better than it did the HD800, but at the time I had the HD800 the headphone amp on the Oppo was not putting out as much power as it is now. They did something with firmware to increase the potency of the headphone amp.
I will get a good comparison between the TH600 and the T50RP tomorrow. Sources will be Oppo BDP-105 headphone amp, and ALO Pan Am with and without the Oppo BDP-105 as a DAC.