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