To DAC or not to DAC ?

@decooney

I attribute the lack of significant difference between the GW and WE tubes to them being in a tube buffer output. I wouldn’t expect a tube to make as much difference as it potentially could in something like a Jolida FX Tube DAC. I am using a 3 foot Blue Jeans Cable silver plated coaxial cable. On a whim, I opted for the silver plated cable vs. their standard copper version.

Take a look at the Simaudio 390 or it's predecessor the 350. Excellent preamps with very good DACs on board. Really, it depends on your listening preference. If your world is digital it's worth going bigger. The 390 gets you a full use preamp, for not too crazy money. Both it and the 350p are highly regarded. I would agree overall your preamp is most likely the thing to upgrade first. 

I have owned a McIntosh C220 for about 10 years.  Absolutely love it.  

A Mac preamp is of the right caliber for your system. But make sure you audion it or at least a Mac system before you commit. Many people love it. Mac is a well respected and loved brand, but it has a very distinct sound, heavy on the bass, good midrange bloom but soft in details. It excels at playing rock. It may perfectly match what you want, or not. It would not hurt to listen to a few systems to set your direction. Might try, Audio Research, Conrad Johnson, Sim. 

I was in a similar situation; good amp and speakers, mediocre pre, Bluesound Vault (which uses the Node 2i and adds a CD ripping ability). I added a used Benchmark 1 for $300 (at the time), and the difference was immediately noticeable; a big improvement.  I'm told that the later Benchmarks are much better, and have been hoping to upgrade to a $1K to $2K DAC for over a year; the Gustard X26 mentioned above by @yyzsantabarbara is currently at the top of my list, as is the Brooklyn DAC+, but there are SO many possible choices.  When I do pull the plug, I'll be surprised if the improvement is as noticeable as it was from the addition of my Benchmark 1; I'd strongly encourage you to get a better DAC than the one you have in your Bluesound 2i; Your range of $500 to $700 should work, expecially if you buy used.  Or, if you're willing to spend more, get a pre with a good DAC in it; either way I'm sure you'll enjoy the difference!