RS6 vs P6 Pro - to my ears while using Traillii, I hear a similar soundstage expansion and overall technical performance. The biggest difference here is in the impact/weight of the bass, being more elevated in P6 Pro. Also, more thickness in lower mids (P6 Pro), giving the sound more analog body and warmth, which makes RS6 sound more neutral and slightly more relaxed in comparison. That's just based on sound performance and while using Traillii. As far as overall DAP performance, P6 Pro is playback only device with Bluetooth Rx and limited user interface, while RS6 is a fully featured Android DAP, plus, P6 Pro cost 2.5x more.
Do I think RS6 sounds better than P6 Pro? No, I don't. But I also found that P6 Pro pairs up better with brighter and neutral tuned IEMs, while not so much with other IEMs that have a warmer or fuller body tuning since it kills the resolution (to my ears, warm on warm is not a good match). RS6 would be more universal in pair up with IEMs across different sound signatures. And if you are streaming or want a proper file sorting/handling with a proper user interface, RS6 is head and shoulders above P6 Pro in that aspect.