It never ceases to amaze me how quickly people will identify with a brand and fight for the glory of that brand - as if one company had invented the headphone. I own a bunch of Grados - iGrados, SR-60s, SR-80s, SR-325i's, RS-1's and GS-1000's. I like Grados, which is why I have my little collection, but it's not as if music isn't music unless it's being played from a Grado. Sennheiser makes great headphones, too. If there's a difference between the two makes, it's that Grados are low impedence, making them easier to drive, while Senns have a longstanding reputation for being about as neutral as it gets.
There are lots of elements to getting decent sound, one of which is plunking down for a decent set of cans. What also matters is the source material, the playback unit, the interconnect device and the amp. They all matter. Although each manufacturer has its own "house sound" (or at least preferences or qualities within a certain range), the differences between manufacturers (or within similar units along the product line) is overblown. Of greater importance is whether you've invested in a decent set of cans or whether you're expecting to get $500 worth of sound out of $5 worth of headphones.
I started upgrading my headphones - from the $49 iGrados to the $1,000 GS-1000's - before I gave much thought to the role of interconnect cable and headphone amp. Having recently upgraded in those departments, I found my weak link to be the source material, itself. Because of iTunes' convenience, I have a lot of 128k tracks. I, too, looked into upgrading to 256k tracks but something - probably pride - kicked in. Why should I pay Apple a second fee when those b@st@rds sold me stripped-down music to begin with? I have since started buying my music from Ebay and other outlets where I can get the cd for a discount. The difference between 128k and 1000k is real. It only takes a few minutes to import an entire album but the end result is more than worth it. I get better bass and more sizzle at the high end, as well as more headroom.
I'm not going to replace everything with cds, at least not right away. I'm reserving that option for new music first. But going lossless is the cheapest way to uprade, and one that pays immediate rewards.
On the "best bang for the buck" homefront, I performed an experiment on a pair of SR-60s. After discovering some sabotage on the early iGrado (where the open-air backs weren't really all that "open"), I decided to remove the rear grill from my SR-60s. This left nothing to produce the resonance Grados are designed to minimize. To make it work, I had to superglue the cushions to the headphone assembly. I did this after switching out the cushions (from the L-Pads to the doughnuts). To my surprise, the resulting SR-60s became measurably clearer and uncolored. And where I'd been led to believe that my bass would suffer, I found it better. Because my bass was only what the driver, itself, had created - not some kind of bass reflex amplified by the rear air chamber - it was cleaner and tighter.
Before you plunk your money down for either an SR-225 or an SR-325, you might want to try what I tried. There are links where you can go through a list of "Grado mods," including instructions on how to remove the rear chamber. If you're brave enough to remove the rear air chamber, and then superglu the chambers to the forks on the headband, you will be pleasantly surprised. The effect is remarkable.
(You can also put a gummy, sound-absorbing, material on the back of the driver's rear center, which will cut down on resonance from vibrations on the metal back.)
