Digital Upgrade Path

Hey everyone - a few months ago I embarked on a rather significant full system makeover, starting with building a pair of the excellent Bitches Brew open baffle loudspeakers. These are a three-way high efficiency design that rely on a MiniDSP digital crossover and DAC. I recently changed my amps to a pair of Audiophonics Purifi 1ET6525SA Class D amps. These amps replaced a Aleph J and a McIntosh amp I was using. Initial impression of these amps is...pretty amazing. Anyway, I love these speakers and the flexibility they are giving me to tailor the response to my room. But, from a digital front end perspective I'm now locked into a single DAC, the MiniDSP. I'm running a stock Bluesound Node 2i as my streamer with a Pangea digital coax cable. I used to use a Schiit Gungnir multibit DAC. The Bleusound 2i does not support USB out. Questions:

  1. Would it be worth upgrading streamers to one with a USB out to feed a USB signal to the MiniDSP? I'd be looking at something like either a newer Node or a Wiim Ultra. Does USB offer an audible difference over coax in your experience? This would also open up the option of inserting something like a Denafrips IRIS in the chain down the road.
  2. If I don't do that, I'm thinking of upgrading the power supply in the Node 2i using one of the Teddy Pardo kits, and maybe the digital cable.
Where would you go with this digital front end at this point...and let's say we want to keep the spend under $1,500 for now.
 
IMHO, MiniDSP is consumer grade mid-fi stuff. Not clear if using USB to feed it would offer much advantage since there are so many other shortcomings with it. Maybe worth trying USB sent from a PC you already have to see if any benefit.