Hi Tom,
Thanks for the kind words and it's always nice to meet a fellow audiophile who share the same interest!
Anyways, my primary reason for choosing to buy the HDP is because i'll be moving around quite a bit and need a transportable rig (DAC/AMP combo) but still wanna retain some decent audio quality.
My initial concern was whether the HDP would have enough juice to sufficiently power the HDP since to me, synergy is a matter better left to more seasoned head-fiers with deeper pockets. And my answer in short is, yes, the HDP definitely have enough juice to power the HD800s (300ohms) to deafening levels. I'm pretty sure the HDP can drive the highly inefficient Hifiman HE-5 as well since i'm using foobar with the volume attenuated to -20dB and the volume pot just slightly below the half-way point.
To be honest, i've yet to own any other difficult to drive phones and the only other proper headphones i've owned are the SA5000s and the SRH840s. Both pretty easy to drive and the HDP does drive them with ease.
The HDP is a really neutral sounding SS amp and since i've yet to compare it to a tube amp, i wouldn't go so far as to say it sounds cold/analytical since i can't really tell. It just sounds clean and transparent to my ears. So as far as preserving the Sennheiser sound, i think the HDP will definitely do a more than decent job, especially for new head-fiers like myself since it is really neutral and doesn't impart any of it's own sound characteristics into the music.
Cheers!
Jeremy