They’ll probably be too quiet for you imo (depending on what you’re plugging them into). If you’re fine at listening at a volume that might be too low for you then not getting an amp is fine.

As for sound quality improvements, my DT990 (basically the same as the DT770) gets a little bit extra bass and a bit more clarity in the music when you get an amplifier. It’s pretty noticeable in my opinion, but not necessary at all