I’ve got a Ti9 hooked up using REL’s proprietary cable which taps off the speaker terminals on the amp. Designed to integrate into a 2 channel system more evenly / musically. The subs can also be hooked up at the same time for HT via LFE / to the AVR receiver.
OP - best advice I have seen is cal REL, they are very helpful. If 2 channel listening is your main goal, at first anyway, use REL’s proprietary system to hook the subs up, you’ll do that off the Parasound Integrated. Get them both working, experiment with placement and settings. The TI series will work with HT but it’s claim to fame is 2 channel and their unique hook up / integration with the amp / speakers. You’ll find many posts / reviews where adding a second REL sub to 2 channel listening has taken a great set up to the next level, I’m sure REL can help get you there. Make sure to take advantage of their recommendations, again, these subs are designed specifically for 2 channel and their reputation is built on seemless integration, following their set up guidelines is key. I find mine is fantastic for music / 2 channel and forgettable in my HT, if I can’t have my cake and eat it to I want it rocking in my 2 channel.