There is only one way to connect a FiiO JM21 to any amplifier.
For example, use the Fiio LR-3.5A audio cable ( art Galaxus 43488541 ) and you will be able to
listen to "recorded" or "streaming" music (e.g. Qobuz) from your JM21 on your amp.
The other option is in USB DAC mode on a computer and it then works like a sound card.
Apart from these 2 options, there are no other possibilities for the JM21.
DACs are headphone amplifiers.
DACs are designed to transform a digital signal coming from a computer
into an analogue signal.