i've heard the sig pros and missed the only chance i'll get in a long while to listen to the th-900's, the sig pros are probably one of the best portables you can buy, quite open sounding and good soundstage for a portable. sounded balanced overall to me. the fostex i wouldn't reccomend for portable because they look to be the exact same design as the d7000 which have a very loose seal.
Thanks for that mate, well guess its a beyer vs ultrasone shoot out then, wallet can't complain about that... But I'll probably end up gettin the th-900's somewhere down the line, can't resist that urushi finish, it's a work of art