ADI-2 DAC FS often goes on sale for less than 1K and for that price it is one of the best, if not the best device you can get.
It drives HE1000se with no issues straight out of the headphone output with plenty of headroom. It is neutral sounding, but not lifeless - bass is really punchy and you can mess around with built-in parametric EQ or B/T shelf.
It is also reasonably detailed and with good imaging, but soundstage is not very big and you can get similar or even larger soundstage with chi-fi combos costing half the price.