Hey Nocturnal,
If you've read the thread that Grainger linked to, I think you can see that the main issue would be a higher bass roll off. With some cans which are low impedance and low sensitivity, the issue becomes more pronounced.
That said, I used to own a pair of SR-60 (or 80's?) and I found them to be very easy to drive. In fact, I used them almost exclusively directly out of a Walkman (portable CD/cassette).
If it's only the SR-60's that you're worried about driving, I'd build the amp stock and try it that way for a bit. If you listen to a lot of music with significant low bass, you might want to change the output caps to a larger (330uF) Panasonic ED series cap. Take it from someone who usually cap rolls to excess, those electrolytics sound very good in that position.
BTW, I listen to my Audio Technica AD2000's on my Crack all the time and love it. The AD2000 are 40 ohm and the output caps are 100uF. I'm sure that the lower bass is more rolled off than it should be but I don't really notice it (iron-ears?).
