If your jbl 230 is the jbl studio 230, it was reviewed by S&V in 2014:
https://www.soundandvision.com/content/jbl-studio-2-speaker-system-test-bench
Its FR looked very reasonable, but if you listen loud sitting 10-12 ft, then as KEW suggested, set XO to 80-100 Hz (I would say 100 Hz for best result) and forget about the A-S501 as you would end up spending the extra money for no audible gain. The RX-V475 actually has the same vol control/preamp chip as the A-S501 so you do the math..
By the way, you mentioned "seating distance is about 10-12ft and I like music medium to a little bit higher. I listen to -10 to-15db on my Yamaha avr. " That may be loud for you, but you are no where near "0", so it doesn't sound like you need more power after all. Setting XO higher to 100 Hz should let the 230 sing better, not that they are stressed at vol -15.
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