powered sub to an Adcom speaker selector box

Plenty of good advice from the replies. Here's another suggestion that may offer a more simple solution.......

Check out the Outlaw ICBM. It's an active crossover that offers adjustable XOVER frequencies. It is placed between the preout and main in. In addition to many outputs for multiple speakers it also has 2 outputs for subs. So, there's no need for y adapters from the preamp.

The ICBM has been out of production for a while but can be found in the used market. It originally sold for $250. May make your hookup more simple.

Another mention.....do your 901's have a lot of age on them? If so, check on the condition of the foam surrounds. I've been down that road.

Yes one pair (Vl ) is perfect and I refoamed all 18 of the V ‘s. 

IF you go line level to sub, as yogi said

after you split your preamp output into two left and two right, using the fitting he posted, or a pair of Y adapters

https://www.amazon.com/LEIGESAUDIO-Female-Adapter-Splitter-Connector/dp/B07P45DT6K/ref=sr_1_2_sspa?d...

you need to convert one l/r to mono for the sub

https://www.amazon.com/FosPower-Subwoofer-Splitter-Connectors-Extension/dp/B01LZVLBY3/ref=pd_rhf_se_...

elliottbnewcombjr

IF you go line level to sub, as yogi said after you split your preamp output into two left and two right, using the fitting he posted, or a pair of Y adapters ... you need to convert one l/r to mono for the sub ...

That is not going to work with most preamplifiers, which typically  have their outputs wired in parallel. If you convert one set of outputs to mono, you'll have converted all of the outputs to mono.

 

That subwoofer has left and right inputs. There is no reason to hook it up any other way from what I showed him for his non home theater preamp!!
https://www.klipsch.com/products/r-100sw-subwoofer