I' m the happy owner of pro900 for... about a year, i guess, and still, the more i listen them - the more i'm in love with them (so, that means my love is infinite, hah).
Nevertheless, im thinking of buying signature pro. Dont know why, just something is scratching inside of my head.
Own the Pro900 and had the Sig Pro and just be warned - the bass is nowhere like the Pro900. I have read that the Sig DJ does so may want to keep that in mind.