An audio DAC HAT is needed for RoPieee, but not for Raspberry Pi. I bought one raspberrypi.org/products/iqaudio-dac-pro and one iqaudio-digiamp-plus, both work nicely.
I also bought one Hifiberry zero since I love the brand, but could never got it to work 
About the bulkyness: I unsoldered the Cinch from iqaudio and soldered a cable directly on the board in order to fit the HAT into the original 7" touchscreen case - where is will there is way 
Others also had no success with a HAT not listed as compatible
If you really don’t like to buy a HAT you can try USB, but please use a decent audio interface and not the cheapest miniTRS dongle.
The internal Raspbery Pi headphones out is not recommended for any quality expectations, even it might be possible using DietPi or other OS.