A few thoughts, at a very high-level:
SMSL SU-8
Competent but only interesting as a cheap-DAC that has decent measurements and XLR outputs. Has issues/audible glitches when switching rates/formats under Windows. Can be harsh, not a great pairing with the RNHP, which doesn’t need more treble energy or any lack of smoothness.
Airist R2R
If you’re looking for a “sweeter” sounding unit, with a more NOS-like sound (it’s not NOS, technically, it does 2x upsampling prior to conversion), it’s a pleasant listen. Was much more interesting in 2018.
Schiit Bifrost 2
Best bang-for-the-buck on the list as well as the most musically involving delivery. Often described as a mini-Yggdrasil A2, and I think it justifies that description.
Denafrips Ares II
Only reason to buy this is over the Bifrost 2 is if you want on-board DSD conversion. Even then I wouldn’t. Lack of ability to demo/return is a major issue here. No idea if the issues I found with the original version have been addressed.
Schiit Gungir Multibit
Not worth it over the Bifrost 2 unless you buy used AND run balanced from the DAC. “A2” version has a signature similar to that of the original Yggdrasil.
There’s one for sale here, at a good price, and from a chap I can personally recommend.
RME ADI 2 Dac
If you don’t need the built-in amp and EQ/DSP functionality, then the Bifrost 2 is a better bet. Micro-dynamics aside, the RNHP is no better than the built-in amp here and more of a side-grade/slight-downgrade from the built-in headphone output.
Best D/S DAC this side of a Chord Qutest or Matrix X-Sabre Pro (MQA).
Cambridge Audio DACmagic Plus
Enjoyable, engaging, warmish Wolfson DAC implementation, subjectively very nice and a good complement to the RNHP. Objectively, a good way from what’s possible at the price.
SMSL SU-9 (maybe out in May)
May be out in May. May be good. May suck. Don’t bet on futures.
Add to your list, the Topping D90 (I’d like this DAC a lot more if “Topping” came up with a second brand with a name that didn’t sound like a low-rent, bad-side-of-town, mixed-cuisine restaurant).