People like to go crazy over amps, and there are certainly subtle differences between many amps (particularly when comparing tubes or simple SS circuits) but these differences are not even close to as significant as the differences between 2 different headphones.
That being said Grados are just not known for soundstage. Upgrading your amp will not help you here. It may help other headphones, and you can certainly use the subtle differences in the way the amp sounds to make small changes in your headphones for the better, but no mater what you do Grados sound like Grados. AKG sound like AKG. Sennheisers sound like sennheisers... you get it.
I would sell the SR225 and buy a set of whichever non-grado headphones you think you will like. HD600, AKG K(whichever version of their top tier headphones you happen to find) Beyer DT880... Pretty much anything but a Grado. They are all a bit more money than the SR225, but with the cash I just saved you on the amp plus the money you should be able to free up by selling the SR225 you should be able to make it happen.
In case you think I dont like Grados, you could not be more wrong. I would without question keep the SR60, sometimes you just need that Grado sound. If you want something more grado than the SR-60, skip to the RS-1. There is no need to own any Grado headphone except the SR-60, RS-1, or HP-1000.
Once you get the (non-Grado) headphones you will probably want to upgrade your amp to suit them better pretty soon, although this is not totally essential. Sorry about your wallet.
Edited by nikongod - 1/28/14 at 6:20pm