Well I have been playing with it for a few hours now and am very impressed. Firstly, it is thing of absolute beauty. It weighs 6kg as well! God knows what they have packed inside but it works wonderfully with my HD650's.
I was a little hesitant about buying it as some have mentioned the Marantz 'laid back' sound, which as we all know, is also a characteristic of the HD650 and I was wondering if both combined might be a little too laid back, but I have been very surprised.
It is hard to describe, but the amp inside is clearly more powerful than the one in the TEAC. I have been using the Marantz on mid-gain, which seems to be the best fit. Apparently the amp can drive up to 600 ohm headphones, which I expect you might want to put the gain to high.
The tone is calm but very detailed all the way through the frequencies, but is strange as what is apparent is that it seems to highlight the air between the sounds, if that makes sense? It makes the Senns seem more airy than I have heard them before but so much richer sounding as well. There is zero distortion or blur between the frequencies and man the bass! It is wonderful and rich but makes no influence on the midrange and higher frequencies.
Negatives? None really. You can hear a click when starting and stopping music but is very quiet and is a lot quieter than the clicks of the TEAC.
It retailed for £679 when it came out and would have been well out of my budget but for what I paid, which was £350 along with my 650's which I bought on here for £150, for £500 in total think I am now done. End game complete.
I'm again going through my favourite tracks with this setup and finding new things with a smile on my face.
The spec sheet is full of stuff I don't understand, like jitter remover and dual master clocks, Marantz HDAM® (Hyper Dynamic Amplifier Module) and HDAM-SA2 modules used in analog circuitry for faster signal transfer and better transient response and ground isolator for USB DAC mode operation eliminates noise from computer connection. Anyway, it works. Getting zero pops and stuff as well which did happen sometimes with the TEAC.