So far so good. Very pleasant to listen to. Different from the uber stack. Gotta go for class now!
Alright initial impressions vs the uber stack. Did comparisons using Flare R2A, Fidelio X2 and my micca pb42x speakers. I 've let the m9xx run for about 12 hours in total. I have a set audition playlist, all songs in wav/flac and I'm using the m9xx via usb using the external power supply provided. Using the default F1 filter with cf off.
One very noticeable difference between the two is the tone. Where the uber stack is all bright and exciting (a little too exciting to me at least), the m9xx is gentler. It is still exciting in the way it delivers all the details but it is less aggressive and brittle. Just very slightly smooth. The difference in presentation was another thing that struck me. The uber stack had everything more forward and in your face whereas the m9xx is more neutral though not at all laid back.
I feel that in terms of bass texture, body and extension, the uber stack edges the m9xx. That is not to say the m9xx doesn't have good bass texture or extension. I can still make out the nuances in Queens' Another One Bites The Dust. Its just that the bass on the uber stack is 'fatter' which at times makes it seem a little slower whereas the bass on the m9xx is faster. I do enjoy the 'fatter' bass more at times. Impact is similar for both too.
Mids are about the same, both very transparent but it does seem that the m9xx has the uber stack beat at this. It's more musical and balanced whereas the uber stack does seem to bring the mids forward slightly.
Treble is also different. The uber stack has more bite and treble presence. It can sound harsh but the treble on the uber gives a greater sense of 'air'. The treble on the m9xx sounds a bit more natural, forgiving, but certainly doesn't have that great sense of air on the uber stack.
Staging and imaging wise, I would say that the uber stack is slightly better. It only has a slightly deeper soundstage. But the uber has a noticeably taller soundstage compared to m9xx. Imaging and width are very close for both amp/dac units.
Technicaly both of these units are quite similar. The main difference is presentation and tone. Other things you should consider between the two would be the cost and form factor. The form factor of the m9xx is quite awesome. Nice large clicky knob compared to the uber stack's smallish knob. The uber stack has less features but you just need to press a single button to change source.
The uber stack will set you back around $350 new with usb and rca cables whereas the m9xx is $500 new. All in all, I think if you really dont mind the form factor of the uber stack, it is great value for money. Your headphone/speaker pairing and sound preference also matters in picking between the two. I definitely don't agree with the forward and bright tone of the uber stack (even with my fidelio x2) so I prefer the m9xx more. Still, there are some things like the bass on the uber stack that I wished the m9xx could emulate. Small difference which can be compensated through good and smart gear matching.
Hope that was helpful!