Hmmmm the bha would probably be a better value, but it will perform significantly worse with the he6 than will the violectric, but for your other headphones it should be a closer race (although personally with the right dac I think the violectric edges out the bryston in technical performance). If you could also score a bryston dac to match that would be sweet. Generally the violectric is going to have the wider stage and presentation, the bryston might have the more organic timbre, they are most likely both similarly detailed, the vio is going to have more grip and control, and also be more dynamic, the bryston might be a bit more forgiving at times, the vio does smooth out the treble a bit though which might make the bryston seem a bit more extended but that will depend on dac pairing
So tbh I just recommend what pairs well regardless of the tech used, there are other options but it really depends. The denafrips have a very full bodied and meaty sound to them, more forward fun and energetic with a smaller stage but more depth, the holo have a neutral slightly warmer smooth sound to them and are pretty spacious and deep, the soekris (can’t speak for the new line) are more neutral bright, slightly analytical and fast, good depth as well.
I think there are a fair amount of os dacs I like, you could get a bda-3 or bda-2 to match if you got the bryston amp and that’s a nice dac that’s neutral smooth and pretty organic. If you could find a used berkeley alpha series 2 dac that’s great for something neutral clean but realistic focused with good control, or a sonnet morpheus might be oversampling and if it is it’s a very quick and detailed dac that’s really revealing without being fatiguing or overly clean. The rockna wavelight is a softer neutral but very organic sounding dac that’s pretty sweet. Also a lampizator amber 3 is great for something wide, warmer, organic and meaty sounding. The xi audio sagra dac is pretty sweet for something clean but lots of control and weight. The wyred4sound dacs are on the warmer more fun side of things as well.
I could keep rattling off dacs I like (and continue to go up in price lol) but in the end it’s going to really come down to synergy here, as what amp you pick is going to really narrow down what dac works the best with it, and then it will come down to budget
You would be moreso moving up to a higher tier of dac with some of the previously recommend dac pairings, so an overall performance bump compared to your adi 2 and it really depends on a specific dac, I don’t want to generalize things. If I had to for r2r I would say the benefits are speed, spatial recreation, and organicness of presentation. For nos it would be natural presentation, a more effortless sound, and perhaps a bit more relaxed. But again it really depends on a specific dac, you can’t tell how it sounds just based off the tech or method used inside the dac
Edit: to further comment on why I think it’s going to be worthwhile to move higher than the adi 2, personally I’m not too big of a fan of the adi 2 if it consider it’s sonic performance for the price. It’s pretty detailed and has a very balanced sound, but imo it doesn’t really hold up well to other options in and above it’s price range, mainly because I think it kind of lacks on spatial recreation, timbre, and proper dynamics. To me I would price it around 500 in terms of sound quality only, what you are paying that extra money for on the rme are all the features for the most part, but if you aren’t an eq fiend and aren’t using it as an all in one, imo I don’t think it ends up being worthwhile