Looking for a sub to put in my amps loop function

@audiokinesis and contuzzi,

Yes, I agree that the subwoofer should not connect directly to the loop which is before the volume control.

6 dB/oct low pass is too slow for a sub. You will have it running up into the mid range. IMHO 12 dB/oct is the slowest I would use. 
Why not just get a sub like a JL Audio with a fully active cross over in it that can be adjusted to suit? If you do not want an active crossover on the DQ 10s just put the right cap on the input of the amp (you have to know the exact input impedance) and passively role the DQ 10s off at 6 dB/oct? If I remember correctly Dalquist's own original cross over the DQ-LP1 had a 12 dB/oct adjustable low pass filter then they gave you a fist full of capacitors to install in your amp. (6 dB/oct high pass) 

Is there a way to set a subwoofer up to stop the nova from amplifying 80Hz and below and still be controlled by the novas volume control.

" Is there a way to set a subwoofer up to stop the nova from amplifying 80Hz and below and still be controlled by the novas volume control."
Yes, by using the Vandersteen subs with the setup procedure imhififan linked to.  The filter slopes are shallow at 6 dB per octave, so imo you might want to position the sub along the same wall as the main speakers and in between them. 

Unless the Nova has pre-amp outputs and power-amp inputs, the Vandersteen approach is probably your best bet.  It's really quite clever, kudos to Richard Vandersteen for coming up with it. 

Duke

If you get a sub that has high level inputs AND outputs, you could run speaker cables from the peachtree into the “in” on the sub, then go from “out” into your speakers. 

Another option is to run your dahlquist’ full range and get a subwoofer with speak-on connections, like Rel or Sumiko.  Sumiko subs are 50% off right now at TMR