So, you sold a 200wpc integrated and swapped to 135wpc separates to get better power and dynamics? What made you choose the Bryston separates? What speakers did you have in your system before the PSBs? Not sure "easy to drive" speakers are going to be your cure. What makes you think that's the case? It could've been any number of things. Seems to me the M6i should have had plenty to drive the Synchrony Ones. I think you should slow down a bit and think through what's going on rather than just swapping out equipment without a clear plan.
That said, I don't think the 804Ds are a good choice. B&Ws are known to appreciate power to open up and sound their best, and I've found the 804s to be pretty light in the bass relatively speaking. I do like your RM25 although I have no idea how they'll pair with your Bryston gear.
You might also consider PMC OB1i speakers. I've seen people very happy driving them with a Bryston B100 that I think has a similar amp section to the one you bought. PMC and Bryston are often said to work well together, and the OB1is should have plenty of dynamics and relatively deep bass with their dome midrange and transmission line design. I also think their somewhat polite nature will mate well with the Brystons that can sometimes sound a little etched or forward with less-forgiving tweets (that would be a concern of mine with the JM Labs/Focal recommendation above and possibly GamuT as well).
I noticed there are both RM25s and OB1is for sale here, which is kinda rare so maybe this is your lucky day.
Something still seems amiss here but tough to comment without more info. Maybe others have some further thoughts. Best of luck.