I run the RA-1 with a Panasonic sl-ct570 portable and Grado SR-80 phones. The sound is amazing. The RA-1 is a very neat little piece that is addictive on looks alone. I also have the Headroom airhead ($100) which is good, but not as good as the Grado - but hell, it's 1/3 the price. Although I've heard that the Grado will drive Senns I think you're better off going Grado with Grado, and take advantage of the built in synergy. Battery life with the grado's is about 50 hours. Headroom's new amps will have a 3 way gain setting which could be fun. They'll be out in a couple of weeks I hear.
If you don't care about the power cord, I listened to the Creek side by side with the Grado and it was very close, the Grado was a bit smoother(with Grado Phones) so that's what I went with.