I was wondering about jitter and really do not know what jitter does to the sound quality so I tried a iFi SPDIF iPurifier. For my systems it did not improve the SQ. In fact the sound became somewhat muddled and not as clear with it so I returned it.
I also auditioned a Bluesound Node2 (not the 2i). Using my external DACs, i could not detect any difference between the Node2 and my Airport Express or Apple TV. Using the internal DAC in the Node2 did not sound as good as my external DACs. I only had a brief audition with the Node2 but I do not think the WiFi in it was as robust as the Airport Express or Apple TV. I did notice some dropouts with the Node2 during my brief audition but I have never had a dropout with an Airport Express or Apple TV over an 8 year period.