To be honest the ATH-M50 is an awesome headphone, but in the end somewhat lifeless. You will probably enjoy the HFI-580's the most. Many Head-fi'ers really give them praise and use you kind of bass-head vernacular.
This is a quote from another thread by iQEM
"why you didn't put HFI580 on your list ? i thought HFI580 are less on the price than DJ1pro...and YES, i have heard em...
i test it A/B (head to head) with my DJ1 (400hours burn-in), and HFI580 (fresh out from the box) easily beat the DJ1 on every aspect...
so, it's time to sell the DJ1 now (for me)..."
Below are a few graphs to really show you which headphone reigns supreme. The frequency response is virtually identical for each headphone. The ATH-M50 still gives a bit more bass. Looking now at the 500Hz square wave response for each headphone you can see that the HFI-580 really has a hard time with harmonic frequencies of 500Hz. This covers big part of the audible range. The Sennheiser and Audio Technica do a much better job at processing these frequencies. Looking at the 50Hz square wave response for each headphone you can see that all three do pretty well at frequencies of multiples of 50Hz. This is your bass range. The HFI-580 ring a little bit more than the others which means you get a little uncontrolled bass. The graphs really do not lie. The ATH-M50's are the better can at reproducing quality sound.
Based on expense you can choose between the ATH-M50 and the HFi-580.
1.) If you plan on being a little more analytical with music and you like to fine all the nuances go with the ATH-M50. It is a more analytical headphone.
2.) If you really want to just sit back and relax and you really enjoy bass more than anything but dot not want it to be totally uncontrolled then the HFI-580 is for you.