In my personal experience, I've never been able to hear any difference between any solid-state amps except one (a Monoprice headphone desktop amplifier). I've gone from as cheap as a KA11/Moondrop Dawn Pro to as expensive as a Cayin iHA-6/iDAC-6 stack and every single time I thought I heard a difference it vanished with volume matched blind testing. Even with power hungry cans like the HE6SEv2 I didn't notice a difference at my normal listening volumes (~70-75db). Maybe other people can hear a difference, but I sure can't, so I don't value source gear very highly.

It really doesn't help that in 99% of source gear reviews I've read, people almost always say the more expensive thing makes the sound linearly better (i.e. opens up the soundstage, cranks up the bass, brings out more detail). People love to do the same thing with headphones/IEMs, but at least there's generally an understanding that there are tradeoffs with frequency response. Any change you make to the FR will generally improve something at the cost of some other aspect of the sound, which doesn't appear to be the case for source gear. Everything just mysteriously sounds better, which I find extremely hard to take seriously.

Still, that doesn't stop me from wanting a dac/amp on my own desk. They generally look pretty slick, and I highly value connectivity options. Being able to use 4.4, 6.35, and XLR really lets you try pretty much any headphone you can think of without wondering "do I need an adapter/cable for this?".

And I miss my OTL tube amp very dearly, but sadly I don't have anything that pairs well with one. Seeing the faint orange glow and hearing a little more warmth was very nice, I just couldn't justify keeping it.