powered sub to an Adcom speaker selector box

I have an Adcom 5400 amp with a Adcom GTP 350 preamp . The amp is connected to an Adcom 3 speaker selector. I also have a Kilpsch  R-100SW as my subwoofer. Can I hook the subwoofer directly to the speaker box like a regular speaker and turn the low pass to around 80hz.  The other two sets of speaker are 901s. I can't find it anywhere but it seems as feasible as wiring the subwoofer in line with one of the speakers as many do. The speaker selector is passive.
 You can't do that. That subwoofer has line level input only. The only way to hook it up is from the preamp outputs to the inputs on the subwoofer.
Line level output from the preamp only!
If I only have one preamp output ( to my amp) on my preamp, am I outta luck for hooking this subwoofer up?
that sub-woofer only has line level in as others have noted.

IF you change to a different sub, some subs, like my Velodyne Servo 1200, have the option of speaker wire inputs or line level in. Adjustable crossover and Volume.

In your setup, the 2 pairs of 901’s always get full range signal via the selector box, and the Velodyne Sub (or similar type) would receive full frequency signal from your speaker selector, then sub use’s it’s adjustable crossover and it’s volume control for only the bass frequencies that you select on it’s crossover. It has speaker wires out, that normally/optionally go to the satellite front l/r, in your case you would not use them.

Another option would then exist: 

1. selector one: full range speaker wires to a pair of 901's
2. selector two: full range speaker wires to sub for extended bass 
3. speaker wires (after crossover, thus no low bass) from sub to other pair of 901's

selector 1, one pair full range 901's only
selector 2 sub for extended bass, other pair of 901's (now they don't try to produce low bass).

selectors 1 and 2: add the above.
@ cunawabi
You can use the subwoofer you have. You will need a pair of y adapters on the preamp. Then you can run another pair of interconnects to the subwoofer. A product like this will do the trick!
Thank you Yogiboy. This seems to be the easiest solution . I appreciate it. 
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


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

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!!
thank you both for clarifications
Got the adapter plugs on the way.