When I first got my HP3 I couldn’t wait to plug them in , so I first tried them with Qobuz HiRes through my phone and tab and I was surprised how good they sounded through a portable device. Then I plugged them onto my Quicksilver Headphone amp fed 192k source material from my DAC and was blown away.
I guess you have to weigh how much better it could sound given your particular headphone. I have two decent phones that I really like and currently my living situation prevents me from enjoying my stereo so spending $1000 for an amp was worth it to me. Plus I have no doubt I will more headphones ...
Take LT’ s DAC for example. It’s a killer DAC in its own right plus it has a really good purpose built headphone section. Does he really need a separate amp? I doubt it because that’s a great sounding DAC. Should he want to better that and add an amp he can , but it will cost $$$ and how much better? Again, your headphone choice I think would more or less dictate whether going down the rabbit hole of upgrading is really worth it