Looking for a sub to put in my amps loop function


I recently picked up a Peachtree Nova 150 to drive a set of Dahlquist DQ-10 loudspeakers and would like to add a subwoofer into the amps loop function to take the load of the 80Hz and below off of the amp and DQ-10s and onto the sub. I was looking at the rythmic audio F12 but would like to know what other options are out there. Thank you for any and all responses.
hammy1750
Audiokinesis is correct.  It will not work like that with the nova.  The peachtree volume knob will not change the sub volume.  There is no way to make it work.  I have talked to David Solomon about this when he was in charge at Peachtree.  
Not possible.
@contuzzi,

Please read the Vandersteen 2WQ manual:

https://vandersteen.com/media/files/Manuals/2wqmanual.pdf

You can insert the capacitor to the loop and connect a subwoofer to preout or speaker output as long as the subwoofer has a contour opposite of the low frequency 6dB/octave roll off induced by the capacitor.
Imhififan,

If I understand correctly, the Vandersteen hookup puts a 6dB highpass filter into the loop, and then the sub is AFTER the loop, and receives a speaker-level signal. The sub’s internal lowpass filter is the inverse of that 6 dB highpass filter. Is the right?

If so, that makes sense to me.

Perhaps I misunderstood hammy1750 when he said he "would like to add a subwoofer into the amps loop function to take the load of the 80Hz and below off of the amp and DQ-10s and onto the sub." I interpreted that to mean the sub’s line-level input and line-level highpassed output would be connected to the loop’s output and input respectively, which would have placed them in the signal path before the volume control.

Edit: Looks like we were typing at the same time.

Duke
@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)