Not in love with my system yet. Help!

I've upgraded my system quite a bit over the last couple of months and I received the components separately due to shipping delays. I got my Parasound Integrated first and all hooked up. It made quite an improvement. I received my B&W 606 S2's a week later. Happy but knew the arrival of the subwoofers I bought would really help make them shine. I received the first of 2 REL t7i subs and hooked it up as directed and the improvement in sound was astounding so I was ecstatic about the thought of getting the second which was a day later. That's where I ran into issues. I have a Denon receiver which handles the HT side of things. My mains are run through the integrated of course and the only source directly connected to the integrated is a Bluesound Node. I have been unable to integrate the subs for music only when I try with both. I can run Audysey and it did an amazing job for my HT but that doesn't do a thing for me as far as stereo. I have bought a UMIK1 and downloaded REW but know they aren't going to give me any way to correct anything. All of my interconnects are unbalanced (RCA) so not sure which unit I should get to help me along. I have looked into miniDSP but think it only has balanced in and outs. I'd like to keep cost as low as possible as wife is on warpath. What unit do I need to get? I get pretty lost in the forums sometimes sorting everything out so forgive me please for asking to shorten my time to get to my goal and going over things that have probably been addressed before. Much thanks!
I say just get a female to female adapter and add another rca run. Placement is very important. You can extend the speakon cable since it is just a signal. Just so you understand I put one sub on each side of the left and rt speaker to add or enhance the sound of my music. I then just added the RCA from the home theater amp.  You can get another sub just for home theater like I did. Like a Hsu. Get ported so you can really shake the room if that’s your thing. 
Thank you @millicurie999 , I will be researching this product. All of this is very new to me and very daunting!

I think I've finally got this to where it's listenable at least and no that with a few minor tweaks I can get it pretty close until I'm able to invest in room correction and room treatment.

Thank you much everyone for your help on this and I have learned quite a bit!
Guys in the comments say, "Mini DSP, 149.xx RCA only. 4 in, 8 out". I don't get why You need to choose a RCA-only connector. That's odd, because you can buy a splitter at 1.09$ which is 10-15% cheaper than RCA only. I did the same when I installed employee monitoring software on my Citrix server
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