I have a FiiO X7, which is very similar to the FiiO Q5 (except the X7 has a music player and MicroSD slot inside). It’s GREAT for bedside or in-bed listening, and I like that it’s upgradable with amp modules. I also enjoy my Chord Mojo.
RCA is an unbalanced, single ended type of connection. RCA is also analog, not digital, so you wouldn’t need a digital to analog conversion (DAC) stage. Coax is digital, and it looks like a single RCA plug, so you have to be careful. The FiiO Q5 also has a Bluetooth receiver, so you can use it with your phone on the go without buying an OTG cable.
Some DAC/amps (like the FiiO Q5, but not the Mojo) have an analog input that lets you bypass the DAC and use it just as an amp.
I don’t have much studio experience... I just know how things connect. What do you do?