First up, no headphone setup will sound any good with poor source input. GIGO applies with a vengeance. The setup here is balanced digital feed out of an Meridian MS600 as part of a Meridian MDMS (used to be more sensibly called "Sooloos") system. It is apodised and upsampled to 88.2 kHz output.
So, one would anticipate a following DAC would have little left to do. Wrong. My experience with the much praised (justifiably so and excellent value) Yulong D100 II showed that. It was very good but lacked the finesse of other DACs here with the M2Tech Vaughan heading the list and a Woo-1 not too far behind. I sold the NuForce DAC9 before I had a chance to compare it so cannot really comment on it except to say it was a very satisfying stand alone DAC/headamp combo.
But my experience has shown that balanced is by far the best option. A SOLO headamp was only here briefly as its unbalanced output, although very clean, was uninspiring compared to the other units here. Of these the now deleted from production Headroom Blockhead Balanced headamp heads the list with a Headroom BUDA not far behind. Obviously there are other highly regarded balanced headamps many have used here al;so giving excellent results.
So then we come to the headphones. The ones used here are AKG 702, Sennheiser HD650 (both unbalanced and balanced) and Sennheiser HD800 (balanced). Of these the HD800 are outstanding but they have an Achilles heel - they faithfully reproduce what is fed in, so if that is at all skewed, the AQ will be similarly compromised.
So my take is that with careful research on used items it is possible to set up an outstanding headphone system (excluding source) for around $3,500. For that you get AQ which will blow away $3,500 spend on an amp/speaker system.
But that is just my opinion based on limited exposure to items owned but after extensive research. You can get better for more than $3,500 but the law of diminishing returns sets in with a vengeance as I have found.