You should get a speaker amp now since you're eyeing tungsten. I would help you reduce the burden of V590Not really but it is inefficient to a point where it can take power from speaker amps as well and not break a sweat. But if you do connect it to a headphone amp that has more current drive, it should work well. I'm currently using it with Auralic Taurus MK2 and Violectric V590 V2 and it sounds brilliant.

Speaker amp for HE6SE is a thing, most of the HE6 owners would attest it, but with IHA6, I wouldn't go past 12 O clock on High Gain + High Current mode.