I have a similar setup. I have an RT85 with a Yamaha AS701. Prior to the Ultra I used an Ifi Zen because I didn't care for the S701 photo stage. With the Ultra I have tested the Ultra's phono input, as well as running my Zen into the analog line-in. In order of preference:
1) RT85 -> Zen -> S701 (sounds the cleanest to me, keeps everything in the analog realm if that's your thing)
2) RT85 -> Zen -> Ultra line in -> analog line out to S701.
3) RT85 -> Ultra phono input -> analog line out to the S701. (Not a fan, seems a bit flat compared to 1 and 2).
I am currently using #2 for convenience.