I have no illusions about getting sound that comes anywhere near SOTA, but would like to enhance movie viewing, and retain the sound of the existing second system for music listening. I welcome any thoughts/suggestions re processor, speakers, set-up, etc.
You may be surprised....a lot! (Especially if you are digital centric in your program material).
Find any pre-pro with Audyssey XT32 Pro (I use an Onkyo in my music only 2.2 main system). These are available from Onkyo, Integra, Marantz, NAD and Denon, and tend to cluster between $1500 and $2500, tho some go much higher. Audyssey will calculate and implement a digital domain x-over between your Arrow mains and the new subwoofers. It will also provide room correction which, IME, cleans up bass response in a startling way.
I found the performance so impressive in my HT room that I ended up effectively ditching my all traditional high-end electronics (ARC, Joule, Cary, PrimaLuna, et. al.) for Onkyo electronics. I'm 100% certain that not everyone will follow suit, but you might want to remain open minded. A room corrected, seamlessly integrated full range sub/main system can become really addictive.
Good Luck,
Marty