Theoretically better to connect my subwoofer from preamp out, or from outputs on my amps?

I have the option to either drive my Mini DSP SHO subwoofer crossover/dsp from a second set of balanced outputs on my preamp, OR from the set of balanced outputs on my Parasound JC1+ monoblocks. I realize the obvious answer is to listen to both configurations, but I begin to  crossover at 35 HZ as my Sasha 2s play very low and I want to compliment them not truncate them with the crossover.  I choose not to run the mains signal though the crossover. This is why I say this is a theoretical question as I may not be able to hear the difference. (so maybe it doesn't matter, but its on my mind) I'm waiting on a pair of new cables so I can't test listen right now, but was wondering if there is a technical advantage to one approach over the other. I think this tangentially touches the REL sub wiring design theory as they seem to feel quite strongly that the mains and the sub should be seeing the same signal at the same time. Going in one cable socket on the amp then out another socket on the amp to a crossover DSP isn't exactly like the REL approach, but its similar in a way.  On the other hand sending the output to both the crossover and the amps at the same time makes sense too from a timing perspective. Parallel paths versus serial. You know how we can be when thoughts start swirling around in ones head! Just wondering if someone out there has thought about this already and/or has technical knowledge about the best approach.  Thanks for your time and thoughts. 
No difference. And REL is blowing smoke. Don't inhale.
Cable has resistance, inductance and capacitance. IF you want the mains input and the sub input seeing the same signal at the same time,  theoretically you should use same cables with same length to feed the mains and sub from preamp outputs.
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Pre outs, quieter, cleaner, tighter and less coloured.
You don’t want your poweramp driving your speakers and another poweramp, especially if it’s tube.
I’ve got 2 subs on my second system, and driving them with line level is much better than from the amps.
 And there’s one less opamp (IC11A) in the signal path as you can see when you use line level.
Cheers George

Put a cap in line to your amp and you have a 6 dB/octave high pass filter. 

Now you have a truly biamped system with remarkably more dynamic range.
I prefer using the speaker outputs so loudspeakers and subs get the same flavor of my system. Using the subs crossover is optional. 
+1 georgehifi

Agree, use PreOuts.  Last thing I'd want to do is to route a quality amplifier's speaker outputs and signal into yet another layer of cheap electronics, connectors, and crossover inside a subwoofer, and then on to another set of speaker connectors and speaker cables out to the speakers, thus further degrading the signal/resolution/detail to the main speakers.  Best to try it and compare.  The comparison results can be notable. Good Luck.
Thanks everyone, the collective does not disappoint!!