CONNECTING A SUB WHEN THERE IS NO SUB-OUT CONNECTION

Oh, and @patrickalston to your original question, 

Is connecting the sub as simple as using a spade-to-banana connector between the amp and the sub?

I think the answer to that is yes. Spade end on your amp’s speaker binding posts (or on your speaker’s binding posts, if they take spades) and (i think) standard speaker banana plugs into the speaker-level input (one channel only) on the back of the subwoofer. The “micro-site for your subwoofer https://products.martinlogan.com/dynamo/ says that the speaker-level inputs require bananas.  (If your speaker’s binding posts have available bananas plug inputs, you could just go banana-to-banana into one of the subwoofer speaker-level input, i think.)

I didn't take the time to look at your preamp, amp, or sub but I've definitely run into similar situations in the past. 

I've done the splitter cables coming out of the preamp to amps & subs. This doesn't work well for all components & impedances. 

I've done the wireless connection to the sub..which still needs the signal plugged into the transponder that wirelessly sends the signal to the receiving device plugged into the sub. This also involves plugging extra devices in somewhere. 

You can wire directly from the amps speaker outputs to sub. 

I have found something that I prefer over these others. SVS makes a line level device that wires/connects to the left & right outputs on the power amp. And then allows you to run rca cables from this device to your sub. No balanced outputs though. 

It's a sub $100 device that works. 

Get that second sub before you do damage to your amps. Then connect each sub’s high level input to its respective amplifier. I had this dilemma with my REL Classic 98 and pair of Quad 303 mono amps.  Fortunately my preamp has both balanced and unbalanced outputs, so I run the amps off the XLRs and use the RCAs to feed the sub with a Y connector. 

When I first bought a subwoofer, I ran it off the variable preamp outs.  Now my subwoofer is behind my listening position and I am using the SVS product that @mattw73 mentioned and it works great. 

@buellrider97 wrote “I’m ASSUMING that you are just experimenting with a sub on hand to see what it sounds like.”

RESPONSE:  I selected the Martin-Logan sub because my main speakers are ML Electrostats.  I wanT to ensure that I used subs that would match the panels’ speed. My brother has MLs, Maggies and uses an ML sub with success.  I try not to experiment and buy the right product once (well, except for my streamer which will be replaced—I’ve already hinted to my wife what I want for my 60th birthday).  When I purchased my CLSs decades ago, there was no sub that could keep up with the panels, but I was seduced by the CLS’s magical mid-range and have rarely been tempted to move away from them. 

@kirkwallace wrote “ REL recommends one subwoofer per monoblock.  So the advice above and what I’ve written below still is correct, but you would chose just right or left channel to connect to a single subwoofer or transmitter. “

RESPONSE:  I’ll attempt this approach later today. 

@mattw73 wrote “ SVS makes a line level device that wires/connects to the left & right outputs on the power amp. And then allows you to run RCA cables from this device to your sub. No balanced outputs though.

RESPONSE:  I’ll look into this.  

@dynacohum wrote “Get that second sub before you do damage to your amps.”

RESPONSE:  I’ll probably pull the trigger this weekend on a second sub.  I hope adding this subs will give be the  low end that I’m looking for so that I can stop looking for new $peaker$.