HE-400 deserves a DAC, I have O2 amp/dac combo. I remember reading on this forum that sound cards are designed to perform many different things with sound, like recording, editing, etc.  DACs are highly specialized. 

I believe O2 is not powerful enough to drive HE-6, but matches perfectly with my HE-400. I don't really know how power-hungry LCD-3 is, but probably similar to HE-6. 

My current set-up: mostly FLAC source files, JRiver player streaming to JDS Labs Objective2+DAC at 24bit/96khz, HIFIMAN HE-400 (rev. 1). I just ordered angle pads from Lawton Audio and am in the market for replacement cable (my stock cable is literally hanging by a thread).     I have been...

I used to own ATH M50. They are fatiguing for long listening sessions (mostly because of strong clapping force) and the sound is just too analytical - it's a monitoring hf after all. 

Hifiman HE-400 is known as a good technological upgrade to HD600, so she could well like them. I bought them recently and love the sound. I think it is wonderful for well-recorded and complex electronic music, but with poorly recorded and heavily compressed EM it may not sound as fun as some...