I'm not sure how much time I can spend in writing my impressions, so I'll write as soon as it comes up to my mind nevertheless I don't have much to tell.
I'm trying M as a pure source to feed another headphone amp. The amp is April Music Stello HP100 and the headphone is HD600, so you will be familiar with the signature of my cans. HP100 has a reputation of sounding neutral. Its input impedance is 1M ohm so I expect it will compensate my cheap Y cable. (Sorry I don't have an audiophile Y cable right now.) I'm using high gain mode of HP100, volume is at about 9:00 and M's volume is full.
The resulting sound signature is surprising. It has much sparkle in highs, is a bit too bright to my taste. So called 'digital sound' and 180 degree opposite to 'thick' one. So the instant impression is it's crystalline. But I doubt if it has more information than directly hearing with Fi-ba-ss. The sound of Fi-ba-ss with M is very gentle compared to this and I'd dare to call it neutral. Considering my preconception about the signatures of Fi-ba-ss and HD600, the result is almost opposite and I'm surprised.
Anyway the sound of HP100-HD600 has some (important IMO) common things to the Fi-ba-ss. The most striking common thing is their 3D sound staging. I'd not say if the stage is wide or not, what I can say certainly is that you can know the locations of instruments and their relationships very clearly and with much precision, even though their sound signature is quite different.
Another common thing is the feeling of tempo of music. I believe that we tend to feel that the tempo of the same music is slower when the sound has less noise and more information. This is common in both of Fi-ba-ss and HP100-HD600 sound with M in spite of their different signature. Usually, if the treble is loud, the tempo feels faster, but this is not the case with M-HP100-HD600. Very composed and non-hurried tempo while its sound signature is quite treble empathized.
I believe this result implies something about M's sound signature.
Edited by gracky - 5/14/14 at 8:20am