Subjectively, I think the pi + I2S DAC is the simplest and most dynamic configuration in my office system.
Hard to compare it to the Teralink since it normally feeds into a Beresford Bushmaster DAC which is a very nice sounding DAC imho. But there are more conversions going on there so maybe yes it does sound a little flatter.
My office hifi is not the best resolving system (SMSL SA50 with Teufel Speakers and a mish mash of assorted cables). But definitely, the pi + I2s sabre DAC used over Shairplay is a very good sounding configuration and it replaces a DAC, Teralink converter and a Airport Express. It is very robust. It has been running for days on end without the slightest hiccup.
If I put the pi+I2S DAC into a more resolving system with dedicated cables it comes very close to a Yulong DA8 DAC fed via USB. My brain is trying very hard to fault the pi + Sabre DAC because it is about a 1/10th of the price of the Yulong DA8 … But I think the Yulong does have an edge in refinement and dynamics (expected) but is very close.
In another Volumio setup, I had the Yulong fed via a cubox-i2 (Shairplay - USB - Yulong) which worked great and replaced an Airport Express and gave me the possibility to use the USB port of the DAC (Airport Express only has a optical out) and higher sampling rate of 48kHz vs 41kHz. Funnily, when I use the raspi in place of the cubox I only get 41kHz.