Robm321:
I actually have owned two pair of HD 650's so far, as well as a pair of HD 580's, and I am quite familiar with their line. I am less familiar with Grado, but I have heard several of their cans (but only as high in the line as the SR 325) with the RA-1. For me they were just too warm, too far off an accurate representation of the music. Perhaps I would really like the RS-1 specifically, but given the Grado house sound, I suspect not. But that is just my taste, and I have no problem with you or anyone else differing. As I said, people who do like the RS-1s seem to like them passionately.
I agree that the Sennheisers are not without problem - I find them quite laid back, and for some people that can equate with boring if paired with the wrong amp and source. But I would stick by my recommendations for Overhang not to buy the RS-1 unless he has heard it and knows he likes it better than the much cheaper Sennheisers. This just makes sense, especially given that many people I know of who have heard both the RS-1 and the HD 650 prefer the latter. And if you buy the HD 650's for $300 new on ebay, you can unload them for $275 used on audiogon if you don't like them. I don't think the same opportunity exists with the RS-1. This is the jist of my argument for someone just getting into high end headphones.
Oh, to Overhang I would also say if you dont buy the RS-1, then definitely look at some other headphone amp options. The RA-1 was designed to mate with Grado phones, and other amps do substantially better with Sennheisers, at least to my ear.