And as far as "His preamp does not have a subwoofer out." just use one or two of these better to have two subs.
https://www.ebay.com/itm/AudioQuest-RCA-Male-to-Two-RCA-Female-Adapter/133357704249?hash=item1f0cbd1439:g:3CoAAOSwAbxeaHtT
Cheers George
https://www.ebay.com/itm/AudioQuest-RCA-Male-to-Two-RCA-Female-Adapter/133357704249?hash=item1f0cbd1439:g:3CoAAOSwAbxeaHtT
Cheers George