R2R Dac choices.

I second your consideration of the Adagio + Ambre combination and @nitewulf  's personal recommendation. 

You have a number of great options in the price range you are looking at (based on the pricing of the Metrum products).

Don't overthink it. Choose and establish a new reference point.

MHDT for the win..........

It doesn’t have a volume control so you’d have to add a preamp as you mention, but the Schiit Yggdrasil or Gungnir are worth looking at. I have the Yggdrasil and a Freya Pre and a pair of M700 monoblocks. A friend of mine has the Gungnir and he enjoys that, too.

I think you should first decide if you want a separate preamp in your system or not. Part of this can be done by looking at measurements, but the other part is personal preference and system dependent voodoo that you won’t know until you try. If it’s me, I choose a separate preamp, but at the very least and if you’re not sure I’d arrange to demo an Adagio (thru Hifi Heaven) and demo one or two good stereo preamps at the same time. I suspect you’ll know almost immediately which one you prefer, and my bet is it won’t be close.  If it turns out you prefer a separate preamp then return the Adagio and get a Pavane.  But you’ll never know if you don’t try. Best of luck whichever way you go.  BTW, I think it's a good bet you'll really like the Adagio or Pavane.  My only thing is I hear the Jade/Onyx get awfully close for much less $$$.  It never ends.  Ugh.