It is interesting that you state that you have no experience with RPi implementations, and yet you’ve already decided that you want i2s connectivity. What led you to that conclusion?
The Allo USBridge Signature has no external i2s port of any kind, so as cwichura suggests, you’d have to use a compatible DAC HAT connected via the internal 40-pin GPIO. Allo’s own Katana DAC would likely work here (check with Allo to be sure). The result would unfortunately look like a high school science project, however. As for using a USB to i2s converter…I can’t imagine any benefit from this. The same thing happens inside any USB DAC.
I would strongly suggest that you start by reading the below-linked article as well as the numerous comments…it will shed some light on i2s and how it became an audiophile darling, as usual without any sound technical basis:
Study: Is i2s interface better for DACs than S/PDIF or USB?