You don’t need TOTL gear to have “the best” sound, for you. Especially if your preferences don’t line up with a predefined frequency target (like Harman). Diminishing returns hits hard around $800 or so, for both headphones and IEMs, but it starts even lower than that. Play around in the budget price bracket, find out what tunings and technical proficiencies you like the most and then if you still got the upgrade itch, now you have a better idea of what to look for in higher end gear. You should also not buy anything that’s so expensive that you’re afraid to use it.

Also, don’t go crazy on amps or DACs right out of the gate. Find what is generally considered “great for the money” and stick with that at least until you’re pretty sure you’re settled in with the headphones/in-ears you have. You can spend a hell of a lot of money on amps and DACs for almost no benefit over something reasonably priced and well liked. The main thing to keep in mind when shopping for this stuff is what kind of tonal shift does it impart. I keep running into amps/DACs that roll off the treble too much making my headphones sound darker than they should. Some like that but I don’t. Maybe you will, maybe you won’t. Won’t know until you try it whether you want a tell-it-like-it-is dead neutral amp or a warm/dark amp or whatever.