Do I really Need a Digital to Digital Converter?

There are two Isolators who make a big difference: Intona on USB with short (!) Intona cables on the link to the DAC and Pink Faun on the Ethernet cable from the router. There is a further way of improving the USB connection by adding a reclocker, e.g. InnuOS Phoenix or Mutec. The digital to digital converters are actually decoupling clocking between server and DAC compared to async USB, so assuming your DAC has a decent clock, that is really not advisable.

So opinions seem to vary and with no real consensus it probably means I should consider getting a used DDC and if it doesn't improve things in a worthwhile way, I can always resell it at minimal to no loss. From my understanding both my streamer and DAC implement USB in a very favourable way and this is how I do connect them. I have tried other DAC inputs (AES and Coax) but have preferred the USB route. I mostly stream Tidal but also play music from an internal drive in the Auralic G2 where I have some files of higher than CD resolution.

There is never a consensus lol that's the fun of audio. You have an excellent streaming/digital setup you can enjoy the great sound you're getting now or tinker. Either way have fun and report back your findings!

So opinions seem to vary and with no real consensus it probably means I should consider getting a used DDC and if it doesn't improve things in a worthwhile way, I can always resell it at minimal to no loss.

That was exactly my plan, but after hearing my Pegasus with the i2S connection there was no way the Iris was going anywhere.  Lots of diverse opinions here, but I’m the only one actually using the same DAC as you so perhaps you might consider that for what it’s worth. 

Soix has a good point, same dac, maybe same result. The search begins