Once again mate, thanks! I need to pull the pin and decide now... What will my PsyTrance-Minimal head thank me for... Been looking at the Beyer DT770 as well. You recommended them earlier. Just wondering how hard they "slam" in terms of bass kicking in. I know the Pro 900's will win here, but if it's not by much, and the Beyers to everything else better, that might be the tipping point for me...
The PRO900 has way more mid-bass slam, so it will immediately sound bassier. The DT770 is less bassy in general, it's bassier than neutral, but it's not overly bassy I find. It becomes bassy with a Fiio amp though with bass EQ turned on (+3 db does a world of work for bass). I prefer the DT770 myself simply because the PRO900's mids had vocals sounding weird, distant, dull, while stabbing your ears with treble so everything had too much edge and you couldn't listen at higher volume levels without fear of getting a tizzy treble spike. The DT770 has better mids, vocals sound great, realistic, not dull and removed, and the treble is bright, but not overly bright, so it doesn't fatigue me the way the PRO900 did; also with the Fiio, I find them to be a touch on the dark side, so the treble seems to roll off a touch, taking any spikes down in treble a slight notch which is a nice match for either headphone. The DT770 is my portable of choice, it's tank-like, has the sound I like for everything, and looks fantastic, simple, not shiny, and matches everything. I had mine recabled to a removeable locking cable that is in black sheathing and shorter (4 feet). Ultimately the Denon D5000 is the headphone I much prefer for what you're looking for. It just has the most amazing bass, wonderful mids, and sparkly treble that just works with all music, but especially electronic. Plus it's gorgeous, woodback, sheathed silver cable, etc. It just doesn't isolate well and it's not a tank, so not really great for someone who bumps around in public a lot. I took mine Kayaking, but that's because I'm silly with my toys.
Ultimately I would suggest you try them out yourself, return the one(s) you don't like the best. I saw a PRO900 for like $250 in the for sale section in great condition. And DT770's can be had for $100~120 generally used too.