Try reversing the bowl pads on your sr225 - it's a bit of an awkward fit but it does tame the brightness and hence bring out proportionally more bass.
If you like that, you can get even more bass by going to ttvj.com and buying his flat pads for IIRC $20-30 (if he still has them; it's been several years for me). Unfortunately I don't feel the sr225 holds up too well to this treatment; the sound gets too mushy and dark with flats. The sr-325, rs-2 and rs-1 are much better with the flats; in fact I hated the stock bowls.
If you want to try the Sennheisers, then the HD650 has more powerful bass than the 580/600. Really nice cans, and far from bright. Find an old Zu Mobius cable to pair with and you've got an audiophile classic (I didn't like any other cable - e.g. Cardas, Stefan AA, Silver/Blue Dragon - nearly as much). I didn't like the HD800 that much when I briefly heard them; they're more analytical/sterile/etched, maybe even a bit bright.
Want to perceive even more bass from the HD650? Pair it with the right OTL tube amp (high output impedance) - the impedance curve of the HD650 when combined with such an amp, will effectively boost the bass without EQ circuitry - the cans can sound great this way too. Even the HD650 can sound a bit dry, sterile and "over-damped" in bass if paired with the wrong low output-impedance/high-feedback SS amp.
And finally - under normal conditions (i.e. barring an electronic catastrophe) you will permanently damage your hearing WAY before your headphones feel the slightest bit of strain. If your ears aren't ringing LOUDLY after a listen - then at least you know your headphones will be OK (same cannot be said for your ears). At least, that holds true for a consistent quality product like Sennheisers...maybe not so much for the small company that rhymes with "Play-Doh". Look up the infamous "grattle".
OR just drop ALL audiophile pretensions and get something like the Beats...I hear they've got lots of bass!
