I am NOT as knowledgeable about this as most here, but will offer that I don't believe you would notice much difference in the sound quality by going to a more powerful and expensive receiver of the same make. Your current one isn't bad at all, and seems plenty powerful enough for the speakers you have now and the future.
My journey to better sound quality is similar to yours. The speakers I'd bought (KEF R500, R200C) had revealed I could go to higher levels but I really wanted better SQ at even moderate to (relatively) low volume levels.
Please consider or at least research going to the Q700 or even Q500 instead of Q900. Because you have a subwoofer, the larger 8" low frequency driver of the Q900 isn't needed, and the 6-1/2" of the Q700 or 5-1/4" LF driver of the Q500 is more than sufficient. Those are a better match to your Q200C center speaker anyhow. My system parallels yours in many ways.
I would encourage you to look carefully at what your needs are regarding Video part of your AV receiver and decide what you really need. I did this and came away from the exercise with a less "video oriented" AVR but with what I perceive to be much better sound quality than the 3 year old Denon it replaced. I'm far more interested in good 2.1 stereo than having 9.2 surround sound. The 5.1 system I have for now will do, my long tem upgrade path will encompass more capability as I see a need for it.
Audition some other AVR's. Include a Yamaha Adventege series, but also try an Anthem MXR310 or MXR510, NAD T748 or T758, Cambridge Audio CXR120 or others and see if you can detect the same kind of difference I did. All I'll say is that I was pleasantly surprised and spent less than a higher end Japanese brand with all the latest bells & whistles that I don't need.
Best of luck to you!