My second-hand HRT Microstreamer arrived today. Been testing it all afternoon with the MA900's. It's very impressive for such a tiny little device. Gives me heaps of power with no sacrifice to sound clarity. It gives me way more power than I really need. I basically had to put my PC's volume down to about 20-30% because it's so damned loud.
Now I'm no audiophile but my first impressions are that the Microstreamer seems to have tightened up the bass response slightly and brought the treble out a bit more. The headphones sound a bit punchier with the HRT as opposed to other devices I've been trying out. (PC onboard audio and Samsung Galaxy 5)
The soundstage is well represented by the Microstreamer. There's a lot of depth and different layers to the music. I really like how detailed the sound is. I've been testing them with songs like Depeche Mode's - People are People & Riders on the Storm by the Doors. I love being able to clearly identify where the sounds are coming from and the imaging is pretty great for a headphone in this price range.
The positional cues are amazing for gaming too. Now that I have more volume I can clearly hear my opponents flanking me or trying to sneak up from behind. The Realtek onboard audio in my PC was just too damned quiet. The HRT absolutely kills my onboard audio.
If I had one criticism it would be that the HRT can makes lower quality music files sound a little harsh at really high volume. It's not really an issue for me though as I changed my music catalogue over from Mp3's to lossless audio a while back.
All in all a fantastic recommendation. Well worth the price.