i have a similar system, to yours. My 450C & 2- 280F’s, 2-250S’s, & 2-svsSB-2000 sounded good with just my denon 6400h AVR powering them, but my system sounds 10 times better, in my opinion, after i added a power amp (Sunfire 5-Cinema Grand). The overall sound was night & day for me. If you add a power amp & buy new, you usually get a 30-day trial/window to test out, & if you find a used power amp, try auditioning it, if possible.
Goodluck man