Best way to connect (and control) a powered sub?

Hello all! Thanks for reading.
My rig consists of the following:

QU-16
Carvin DCML3800 Power Amp for mains (700w/side)
JBL MRX515 tops
Crown XTi1000 for monitors
JBL PRX918XLFW Powered Sub

I currently have the sub connected to mix 4 with just keys, bass guitar, kick drum and our iPod.
I’m looking for a way to pair the sub with the LR fader so they’ll both go up/down in tandem.
Can anyone help me?
Thanks!
Scott

Do DCAs work on the QU-16? Seems like that would be the way to go. Of course, now you need access to the DCA fader, which I believe can be exposed through a customer fader layer.

You can put L+R and Mix4 onto a DCA, and put that DCA fader in the custom layer.