2 subs connected to a 2 channel amp?

The subs probably won't be co-located with the speakers, so I was just assuming you want both left and right signal to all subs. Similar to what you'd do with just a single or with a home theater setup would do with 4 or more (although via RCA).

Chain will be Bluesound node streamer --> maybe DAC --> Willsenton R300

Sub frontrunner are HSU ULS15 or Rythmik F15HP.  Subs have RCA in but the amp does not have RCA out.

People can correct me if I’m wrong here, but couldn’t you do a y-connector out from the Node’s subwoofer output with one signal going out to each sub’s LFE in? I know you can select the type of options for the Rythmik sub, and if I remember, the HSU had an LFE input (Left Input would be used only per HSU). You would then use the Node for its variable volume control.
 

I used to own the ULS-15 and currently own the Rythmik F12G. Both companies are fabulous. I appreciate the Ryhmik’s flexibility in terms of its dampening options (kind of like HSU’s Q-Control), parametric EQ, and variable crossover (HSU 0/180 phase only).

Well that's an interesting idea. Didn't even know it had a sub out until you said something.  :)

So connection to speaker out of the node to the sub, L/R speaker connection as normal out of the integrated amp and then I just need to use the node's volume control.

I will def look into this!!! thanks!

If you want a device to accomplish this check out the dspeaker 8033 sub equalizer.

John - correct on the above if I’m reading it correctly.

Node > sub out > y-connector (male to two female) > separate RCA runs to each subs’ LFE. 

Node > RCA R & L output > Amp R & L input

Master volume through Node’s variable volume control. If the sub’s signal is low (like you’re needing to really push the gain on the subs) you could also play around with another y-connector (female to two males) into R & L inputs of the subs.