I'm sorry Evan, I didn't know about the Sony's, I assumed that from your post, not knowing they have an "upgraded" version as you say. About the high's - the Senn's are already considered to be a bit muffled (which is my experience, too, well, perhaps it's more the MDR-7506 I didn't like so much back then), so, well... Actually this shows once more to me it's down to personal favorites more than anything.
Jay, the headphones will work (right now here with no amp), however the Sennheiser's are a bit difficult to drive, and they will respond a lot better especially in the low frequency area if a headphone amp is used to drive them because of the high impedance (300 ohms, compare e.g.: Koss Porta Pro 65 ohms, Sony MDR-7506 24 ohms). Headphone amps that are considered to work good with the Senn's top models are the X-Can series from Musical Fidelity and the Rega Ear headphone amp, the Creeks are not the first choice with Senn's. I heard neither yet. Please have a look at head-fi.org for further information. However, I strongly suggest to compare various settings of the headphones yourself and to evaluate which could be your favorite and which design is suiting you better. There are not only minor differences in comfort (for long sessions), weight and other things like seperate replacement parts service.
Hope this helps,
PolarBear
Edit: PS: A word about cabling and Sennheiser's: I'm not the only one that experienced problems with the cables Sennheiser's uses, some tend to get loose sooner or later, resulting in odd crackling because the connectors (in the phones) move around a bit if your moving. However I couldn't justify the need of a $300 cable, because there is no sonical difference. Others may widely disagee, but to me an investment of $300 in a good headphone amp is the far better solution than throwing it outta the window for a little wire IMHO. Besides, I had no trouble with the standard replacement cable I'm using now for years.