Standalone DAC upgrade from onboard integrated

I was in the same boat as you and began researching and searching a couple of years ago. The DAC I was using was built into my Bluesound Vault. I's decent, but I was looking for something more. I was considering the following:

Geshelli Labs Dayzie 

Schiit Yggdrasil

LTA Aero

I went to Capital Audiofest and was able to listen to the Dayzie and the Aero. Schiit did not have a presence, but I have the Loki Max and respect what they do over at their R&D labs.

The Geshelli was great as was the Aero, I kept researching and comparing other's impressions of each. Last November, when I was ready to pull the trigger, I went to take a last look at both and the Dayzie was discontinued. Made the decision for me and I went with the Aero. A bit more pricey, but liked the tube stage and the ability to change tubes to alter the sound. Very happy with the decision.

The Dayzie and other Geshelli products allow for similar modifications by swapping op amps. They've come out with a new DAC called the TORC, around $700 depending on options, fully customizable and upgradable. If this is similar to the sound they were getting out of the Dayzie, it's a steal - also if you're looking for a solid state answer.

This is a very new unit, so they are figuring out production times as they are a small family owned company and hand build almost everything. You can check it out here: https://geshelli.com/product/torc/

I might get one for my outdoor system as right now it's running off a Bluesound Node built in DAC. I'm waiting to see reviews once production starts full bore.

Good luck on your adventure.

@phydo 

I have the Node 130 with a LPS upgrade and bought a Denafrips Ares II DAC.  The Ares II is not really a noticeable improvement on the DAC in the Node 130; so if you go Denafrips, go for a used Pontus or higher to avoid just a lateral switch.  After I upgraded my streamer, I put the Node into a bedroom system and didn't even bother to hook up the Ares II.  I'm keeping it as a backup DAC, but probably should just sell it.

+1 for the Cyan2.  And there are plenty of other good options out there in the $1-2K range.  I made a similar move with my office system: Bluesound Node 130 w/PD Creative power upgrade > Cyan2 > Arcam SA20 integrated > Maggie .7 w/ silver jumpers and silver tubes instead of fuses + REL T5/x.  Adding the Cyan2 DAC was an undeniable improvement over both the Node and Arcam internal DACs.  Once you hear it you can't go back!  My office system is a step down from what you have.  I am not familiar with the M6si or its DAC but I am confident you will get a nice bump in SQ with the outboard DAC.  I think your only question is which DAC will have the improvement/synergy you seek in your system?  The only way to know for certain is to try it and you could resell the used R2R if it doesn't deliver the gains you are seeking.

Add a ModWright Analog Bridge and save the current DAC. It's magical. 

I have the LTA Aero DAC and it’s phenomenal.  The ability to change the character with different tubes is also awesome.  Highly recommend the DAC.