Preamp LR to sub?


I plan to use a pair of Velodyne HGS-15s with a pair of Velodyne SMS-1s that provide acoustic room correction to supplement a pair of KEF Reference 1s.  Output to the SMS-1s will be LR XLR from an Ayre KX-5/20 preamp.  But the last time I fired up the HGS-15s I recall hearing a hum from one of them.  If I use only one HGS-15 while the other is repaired, should its SMS-1 receive both LR from the preamp, or does it matter.

Finally, any recommendation for low-pass and slope settings.  IIRC I'd been using 40 Hz and 24 dB.  The subs are mostly activated by organ pedal notes and explosions in movies (HDMI from DX-5 DSD to Bryston SP3 to KX-5/20 by-pass).

db
dbphd
Thanks noromance, that was the essence of my question.  On reflection, I realized that must be so.  I was confused because the Bryston SP3 processor has a single sub output in addition to LR outputs whereas the Ayre KX-5/20 preamp has only LR outputs.  Obviously the SP3 does the summing internally.
If you run one sub temporarily, you should feed it both L+R. Otherwise you’d be only getting half the summed stereo information. In other words, you'll be running as if you'd only one SMS and one sub.
The KEFs run full range.  I was asking about settings for the HGS-15s.  They are set by the SMS-1s.
Doesn't matter. 

I would try without the crossover. The thing with really low bass, you want many different sources. That's why 2 subs is better than one, and 4 is better than two. Crossing over eliminates the KEF from being additional sources of low bass. Running them full range should be a notable improvement.