Your choice of a tube stage DAC is an interesting one. The reviews of the Glass FX Tube DAC/DSD WiFi are good, but have you taken it as far as it will go with the PSVANE 12AX7-S tube upgrade over the stock tube? As good as it is, it is a $900 DAC - a very good one at that price point, but not a $2K DAC.
You are using an external DAC, not the one in the Node. The Node is only a transport. Yes, transports can make a difference, but I would venture that you’d get more bang for your bucks by trying a higher end DAC first, and then later on maybe another streaming transport.
I would also look to a DAC with USB input and configure the Node to use its USB jack as an OUTPUT to that external DAC and make sure the presumably better clock circuit in the external DAC is doing the driving for less jitter, not the clock in the Node.
In the meantime, you might look at doing one of the relatively inexpensive upgrades to a LPS for the Node. This could always be used in a secondary system you have, even if you do buy a better digital streaming transport later. Many swear that it makes a demonstrable difference in audio quality.
Oh, and you didn’t mention which output from the Node into the Black Ice DAC you are using? Have you tried the other outputs versus the one you are currently using? Worth a try. And do you have the DAC set to full volume output to bypass its internal volume control, and only control the volume via the Saga?