After wading through all this it occurs to me that we don't know anything about the OPs system apart from iStuff. Maybe I missed it? Anyway, it's completely unsurprising that a reasonable CD player/transport on a reasonable system would sound better than the iStuff. I've got a kind of mid-fi setup with KEF LS50s, PS Audio Sprout 100 and Bluesound node 2i. My android phone can stream through the Sprout via Bluetooth. The Node 2i sounds far better (yeah, I know, Bluetooth yada yada). I've also got a seriously high end "reference" system also using a Node 2i. The differences are even more pronounced. That said, the differences between the Node 2i and CDs and ripped CDs onto flac files is minimal. And how much of that is imperfect level matching? Anyway, what you've done (I think) is really just take Bluetooth out of the chain. But what's the rest of the system? Getting all kinds of specific advice on streamers, routers etc is, IMHO, pointless without knowing the rest of the chain.
My gut reaction is just get a Node 2i. Use ethernet if you can. Listen and compare. I'd be amazed if it wasn't an improvement. THEN contemplate how much better it needs to be, if at all. If you upgrade just sell the Node 2i. And forget the special audio router stuff unless the rest of your system is very very special (flame on!).