If you use your headphones regularly then a headphone amp would be a worthy addition to your system anyway. I've borrowed a set of Grado SR-80s in the past and they sound amazing plugged into my iPod, but thin, weedy and two-dimensional plugged into the back of my Meridian integrated. While I can't judge your Cyrus, I wouldn't be surprised if you found the same to be true. If I used headphones more often I would definitely be looking for a dedicated amp too. £300 gives you a lot of options, so I suggest you start shopping! Or at least auditioning. Make sure that whatever amp you consider is happy driving your headphones (a quick googling suggests they're 120 ohm). Oh, and I've heard some bad stories about the Grado amp - hardened hi-fi diy-ers have pulled theirs apart to find a cheap and rudimentary amplifier, glued inside an expensive chopping board.