I owned the DACMagic plus for quite some time and it is an excellent DAC. I really couldnt find any fault with it and it was powering my headphone setup and Adam A7x Studio monitors. Also it worked as an excellent preamp. Since the volume was digitally controlled, there was no channel imbalance or sound coloration. Also the USB section worked great and there was no clicks, pops or hums.
On the amp section, i used the Dacmagic Plus to power HD800, T1, RS1 and Q701. I have never heard my RS1 sound better in any setup and it was a perfect match. It was a very bad match with the T1 and i think it was because of the 600 ohm resistance. HD800 was a decent match but i found the setup a bit bright. I guess it was because both HD800 and DACMagic are both bright in nature. It was a very good match with the Q701. So to summerise, as long as your headphone is not bright or power hungry, the DACMagic Plus should do the job very well. I retired my Matrix M-stage when i bought the DACMagic Plus because when i added the M-stage in the chain, i felt like the amp was taming the highs. This wasnt bad because the HD800 benefited from the coloration provided by the M-stage.