off, you should listen to every speaker you can locally. If you have a best buy Magnolia or a local HiFi store. You need to determine the sound you like. If you can describe some of the characteristics like preferring warm, neutral, etc then people can help more.
, going from Bose to Sierra Tower RAAL is a big step up. So the question is do you need that big of a step up (listen to speakers in #1
to determine whether you value a $500 speaker vs $1k speaker vs $3k speaker).
, I have a Marantz 7009 with Sierra 2's upstairs and you will have plenty of power. Downstairs I have Tower Raals and horizon with Emotiva preamp and amp. I have two FV15HPs and am close to 6,000 cu ft (side room is open so kind of an L shape). I value music more so I am fine with these. If i listened to >70% movies and really wanted extreme bass like many on the forum I'd probably go with the FV18's. Regardless, talk to Enrico at Rythmik and he will help. You need to figure out whether you want to pressurize room or really good bass. I think this is a personal decision. I went with the CBMs for surrounds. The smallest cheapest speakers Ascend sells. They are actually very good for the price point and handle surround duties very well.
Personally, I'd probably downsize my fronts to Sierra 2's, maybe snag B stock, and either do a horizon center (probably) or a Sierra 2 center. Plow the savings into 2 subs. Maybe the FV18hps.
For atmos, I've been researching but Emotiva hasnt updated their preamp to handle yet. Most recommend RSL because, again, these are just doing ambient sounds, etc. Don't waste money here. I'd rather go with towers up front and cheaper surrounds/atmos than more expensive surrounds/atmos. I don't have personal experience here.
REGARDLESS, I know I like Ascends. You need to figure that out. Kefs are good speakers, Monitor Audio (Gold +. Didn't care for Silver), and B&W were a few of many that I liked but didn't get. I recommended to a friend the Elacs by Andrew Jones. I think they sound similar to the Kefs. The Kef R towers were solid and if I couldn't get subs I'd probably have bought them. They had weight in the low end (obviously not sub good but still).
I'd also reach out to Rymthik and Ascend if you are set on them. They are EXTREMELY