Don't do that. For one, those speakers start rolling off at 50hz, two, subwoofers are much better at Bass than even the most monstrous floor standing speakers. My advice is to set each speaker to 80hz, unless the speaker is incapable of 80hz, then set it 10hz above the quoted -3dB point.
I would dump the Sony speakers. While they make excellent garage speakers, they're not that great for reference listening. Pretty much any klipsch speaker is going to tonally match another klipsch speaker close enough to blend with the RB 41. Right now you can find a pair of klipsch RB 10s for about $120 new on eBay. I'm currently using them as atmos speakers attached to the ceiling and am highly satisfied with their sound. I get a solid 80hz in room response with them, and being that klipsch speakers are extremely efficient, considering the size of your room I'm sure they will be capable of reaching reference levels with minimal distortion. The other suggestion I'd make is the you either elevate the center to ear height or mount it above the screen angled down. If the screen is acoustically transparent you could also place it behind the screen. Klipsch speakers have an extremely wide horizontal dispersion pattern of 90°, providing a flat off axis response up to 14khz, however, most models from the reference II series have poor vertical dispersion, causing a massive suckout at around 7khz vertically off axis (above and below the tweeter). You say you are on a tight budget. If you can stretch that budget just a bit, a set of R-15ms and a klipsch r-25c will make a massive improvement to your front sound stage. The newer reference series are much more accurate, and the r-25c has a wide 90° vertical dispersion pattern, making placement above or below ear level a none issue. I have no issue reaching peak SPL levels of 115dB during movies in a 20x12 room, sitting 9ft away using the above mentioned speakers. They dig much deeper too, the R-15ms reach about 50hz in room. All three can be had for less than $500 total.
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