You can find people who have owned one or the other over on head-fi.org. I can't think of anyone who has owned *both* though, but I might be mistaken.
You may already have considered the following, but for anyone else who is reading along:
The Grace is does not require drivers, whereas I the Mini-DAC requires that you use Apogee's drivers. Some people have different takes on this, so I leave it to you whether or not this is pro/con. Both should function fine under either Mac OS X or recent versions of Windows.
The Mini-DAC should eventually have a Firewire option card (it would replace the USB card), there is some discussion about it on gearslutz.com - this may or may not be of interest to you. Firewire can handle higher sampling rates than USB (192KHz, vs. 48 KHz)
The Mini-DAC has XLR balanced outputs AND a stereo mini-jack. You could get adapters for either output to allow you to use RCA jacks. Whereas the Grace has only unbalanced RCA outputs. The point being I guess, that if you really want balanced outputs then the Mini-DAC might have the edge.
The Mini-DAC is also at least half the price of the m902, though the m902 has a remote option. Either get a compat/universal one that works with their codes or buy their $150 (US) option.
The discussion over at head-fi.org right now sounds like the DAC in the m902 may not be as great as you'd hope. So unless you have other reasons to favour one over the other - it might not be worth paying twice as much to get the m902, you could instead invest that in other aspects of your audio system, speakers, amp, etc.
You may already have considered the following, but for anyone else who is reading along:
The Grace is does not require drivers, whereas I the Mini-DAC requires that you use Apogee's drivers. Some people have different takes on this, so I leave it to you whether or not this is pro/con. Both should function fine under either Mac OS X or recent versions of Windows.
The Mini-DAC should eventually have a Firewire option card (it would replace the USB card), there is some discussion about it on gearslutz.com - this may or may not be of interest to you. Firewire can handle higher sampling rates than USB (192KHz, vs. 48 KHz)
The Mini-DAC has XLR balanced outputs AND a stereo mini-jack. You could get adapters for either output to allow you to use RCA jacks. Whereas the Grace has only unbalanced RCA outputs. The point being I guess, that if you really want balanced outputs then the Mini-DAC might have the edge.
The Mini-DAC is also at least half the price of the m902, though the m902 has a remote option. Either get a compat/universal one that works with their codes or buy their $150 (US) option.
The discussion over at head-fi.org right now sounds like the DAC in the m902 may not be as great as you'd hope. So unless you have other reasons to favour one over the other - it might not be worth paying twice as much to get the m902, you could instead invest that in other aspects of your audio system, speakers, amp, etc.