Edit: my thoughts on this topic have changed a fair bit, see linked post
That might be a little overkill for the 789 tbh. I would suggest under 1000 if your other gear isn’t at the level that a dac above 2.5k is.
The RME ADI 2 dac is a great option and stacks nicely with the 789. Sounds great and lots of features.
The GUNGNIR multibit is a nice multibit dac in that price range as well
If you really want that super level of performance, the iFi Pro iDSD sounds excellent and has some very interesting features.
I also thought the chord qutest is definitely good, but lacking too many features for me to recommend tbh.
The Holo Audio Spring v2 Level 2 is also a really nice sounding r2r.
There are higher up dacs I believe sound excellent, but they’re at a level that you would only notice a difference with a 100,000 system
Edit: I don’t really think you would need 2 dacs, but there really isn’t a definitive answer if Delta sigma or r2r is “better” since it’s all about sound. I feel that r2r and multibit dacs are usually more colored because of the way they are implemented. But then again something like the iFi also has its own unique sound signature, so if you have the chance, perhaps try some of these out (or buy somewhere that has free returns), see what you like, and stick with it. The RME and iFi (and even the Holo dac I think) have lots of options like filters, buffers, and eq and dsp, so you could always tune a sound to your liking