Is She Who Must Be Obeyed possibly going to be listening with you? In that case you should keep an eye out for amps with two jacks...although even with an external headphone amp connected to your DAC1 you can listen from the DAC1 and from the headphone amp at the same time (which, btw, is a great way to decide whether the amp is better than your dac1 jacks.)
If you budget is that high I can recommend w/o hesitation the Stax Omega II system for around $3k new. Very satisfying for audiophiles relegated to cans.
If you budget is that high I can recommend w/o hesitation the Stax Omega II system for around $3k new. Very satisfying for audiophiles relegated to cans.