Headphones

well you can get the qudelix 5k and eq it is strong enough to power even a couple of headphone out there so it is a good investment for the next couple of year. I recommend it over btr5 because it have plastic shell -less fragile and better connect range. I have the hook x and qudelix and for my experience with those you can find some eq profile that very interesting. My favorite is the Diva profile for vocal and sa6 ultra for instrument track.

No. I refunded mine after a day. My phone was literally better.

Switching to bluetooth dongle will greatly increase convenience.
Qudelix 5k might be able to fix some of issues too by using EQ.

It won’t make a difference sonically.

Do you need one: No.

Does dac amp improve the sound: Yes.

Dongle is fine and if there's something about the sound you don't like different eartips can make a huge difference. That said, I'm currently using a gaming phone so it has a 3.5mm jack but I still bought a dap so my headphones aren't connected to my phone, especially while I'm out of the house. I bought a tiny one, (Shanling m0 pro) and love it. I clip it on the outside of my pocket I paid $130 for it and it's been completely worth it. But that's so I don't have a cord attached to my phone not for sound quality and I'm using downloaded files on it. My dap also works as an external DAC/amp but I've only used it that way to get more power to some over ear headphones.

no

No. Your phone is already enough. Ppl who said otherwise are mega copium. I own DAP (shanling M6) and I dont even use it (regret).

I personally would like more headroom in volume, my S12 needs 100% volume to my listening preferences. So i bought a Hiby FC4 DAC Amp combo which got the balanced 4.4 options for more volume (although the 3.5 got enough juice too).

I personally prefer a non-bluetooth dac amp, purely for bypassing battery usage, i mean i understand the convenience of wireless but i don't want more device to charge.

It all comes down to preferences.

Yes, a DAC/amp will improve the sound quality. The BTR5 is a great choice and what I still use on the go. It is small, powerful, has great battery life and is highly customizable. And bluetooth is just much more convenient versus the dongle if you're moving around.

Get a 2.5mm balanced cable to use with it, that way you can plug into the balanced port which will give you more power which in my experience with the 7hz Timeless make planars sound significantly better. Also, it has its own battery, which will extend the battery life of your phone.

If you want to hear a big difference over the Apple dongle try a Cayin RU6/RU7.

You know what can make them better? Setting them down for a few days or a week and listening in something else (like the AirPods, if you still have them).