^ Listening to my HF2s from the M-Stage right now and I can confirm that these work well very with Grado's. GnR and Scorpions guitar work sound just as crunchy as ever. BTW, this was also a question of mine because I couldn't find a lot information of how this amp (or the BCL) would perform with Grado's. To me, this amp wasn't that expensive, so I just pulled to trigger to find out. Well to my relief this amp does indeed work well with Grado's.
I don't have my SR-80s and RS2s anymore, but I do know (from experience) that you have to be careful with certain solid state amps in regards to Grado's. A bad match can result in awful headaches because the high-mid / low-treble emphasis of these 'phones. My post above regarding the M-Stage with PS1000s also apply to the HF2 (after all, being Grado's they both share similar driver technology).
This amp is smooth, very smooth - you will not get an ear splitting headache from prolonged listening with Grado's. Without proper amping, the lower end Grado's can have problems (comparatively) with muddy bass and congestion in loud passages. The M-Stage controls these aspects very well. The sound signature is a wee tiny bit side of warm (probably from the OPA2132) - not overly warm - but it's a bit deceptive because the midrange and treble are very smooth, yet still very evident. Bass and treble sounded a bit more extended on the HF2.
Finally, the dip switches on the bottom allow you to have a gain of 1. This is really really nice for high sensitivity 'phones like Grado's because you can have your volume knob set at the 12 - 2 o'clock position, instead of the usual 8-9 o'clock position of many other amps. This was another reason I wanted to at least try this amp out. I had considered the Audio-gd C2, but I think that amp's got an insane amount of gain built-in. I know this sounds like a stupid consideration, but if you've got little kids running around the house who like to turn knobs all the way clockwise, it's an important one.
In regards to the SR225i, it's not nearly as bassy as the HF2, but I feel you will still get good results with this amp. You can always swap opamps to tweak the sound a bit.
As an aside, I've got this amp on for at least 36 hours straight now. It sounds smoother and more detailed now than when it first arrived. I am rather amazed at how good it is considering its price. It does everything solidly well with no weaknesses in any one area. This is one of those amps that does really well in bringing out the best (or worst) aspects of the source - digging out the tiniest details, etc. You open up the amp and you are dumbfounded how a cheap (but good sounding) opamp followed by two pairs of transistors can sound so good. It's probably in the details of the implementation - PCB layout, component selection and quality, and those big ass Nichicon caps in the power supply.