This SVS SB-1000 will fit the bill. You have the option of using speaker level or line level inputs!
I'd suggest you talk to the dealer who you bought the speakers from looks like the Dyn subs integrate with the speakers but the web site is not great in revealing all the details. I'm not sure how you'd connect the node to a sub and control both the sub and output volume levels so again talk to the dealer.
Do your speakers have a sub out ? if so use that. if not do the Dyn subs have integration for the speakers? The SV sub can integrate this via the speaker input but since your using powered speakers you wont be able to use that. again talk to the dealer who sold you the speakers.
Oh, and for $500 pick up a used SVS SB2000. The driver is considerably better on the 2000 vs the 1000.
To add to my earlier post, the link would plug into the wall, then you run a pair of rca’s from the link into the subwoofer. Set the crossover and volume level on the sub and then the volume will adjust accordingly when using the Xeo remote! I think using the Dynaudio Link as opposed to going through the node will make your life easier and will also make things run smoother. I looked into connectivity reviews with the Node 2i used to connect a sub and it seems like there are some issues (I have no first hand experience with the node 2i...