Subwoofer to use with Dynaudio Xeo 20s and Bluesound Node 2i

I'm using the Xeo 20s wirelessly with the Node 2i.

I'm looking at options to add a sub.  Dynaudio make a few subs, in their home audio range the sub 3 and sub 6, and in the pro audio range the 9S and 18S.  I'm not sure if any of these are suitable.  Also the sub 3 and sub 6 are impossible to find for sale anywhere.  They're also way too expensive anyway.  The 9S is reasonably priced if this would work...

But I'mm confused on the connectivity.  Would I just connect the sub via the Node 2i sub output?  Or is there an option to connect them directly to the Xeos?  

Also I'm looking for a budget sub really.  Around $500, if anyone has some recommendations.  
This SVS SB-1000 will fit the bill. You have the option of using speaker level or line level inputs!
Rythmik F12 is also at your pricepoint and an excellent sub for the money.  
Thanks, looks perfect.  Still confused on connectivity though.  I think I have to connect it via the Node 2i sub output.  But what type of cable do I need?  
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. 

Thanks will do.

The bluesound app for the node should control volume levels for speakers and sub.  Has an option in the app where you can tick a box to say that a sub is connected, at which point its meant to do some leveling.

You need a “Dynaudio Xeo Link”.  There normally $199.  There’s one on ebay used for $120!

I had some xeo 6’s.  Same story...
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...