How to hook JL F112 sub to both preamp and pre/pro

No, you cannot, you absolutely can get competing signals that can damage the amp/crossover.

I have talked with JL Audio (and Velodyne, and B & W, and Sunfire....) about multiple inputs when I owned an F113. I bought a Rel B1 and sold the JL Audio so I could use one sub for both, with 2 sets of connection. Definitive Technology Subs do this as well.

I really think it's easier, and prob a better set up for a high end system, to buy an external cross over and keep your bad-ass sub like the JL Audio. You are integrating the 2 channel sub anyway, this just take it the next step and takes the lowest frequencies away. If you have speakers that truly go down below 30hrz, you may not want to do that, but then you can just let the full LFE signal go to those speakers anyway without damaging them, and you don't need any connection but the 2 channel, with the processor set to no sub.

Bob, from everything I've read, even the better pre/pros cant compete with a good standalone preamp. Now, to be fair, I havent tested this thesis, but the overwhelming opinion in my research of forums (Agon, AVS, etc) says this is so. Also, adding a good preamp for say 2-3k would be a lot cheaper than paying 8-10k or more for a comparably sounding pre/pro like say a Classe CT or even SSP800, or a Theta Casablanca, or even the soon to be released Bryston SP3 or Cary Cinema 12. Also, the best sound is likely to be from the analog inputs that bypass processing in the these units, and that brings me back to my original problem. I will check out that NHT unit, maybe I can find a used one.

texas, sorry to belabor the point, but i'm very curious on your position where multiple sources to the fathom subs are concerned. if you're still following this thread, would you mind expounding on the circumstances that would result in competing signals? i'm genuinely curious about this, as i ran this way with an F112 without any (perceived) ill-effects for a while after consulting with the tech at JL Audio. am i setting myself up for some issues down the road??

Jeffkad, yes, my preamp (aesthetix calypso) has multiple outputs. i ran the main L/R outs from the HT pre/pro into a bypass input on the preamp, and from there, one set of outs to my main amp, a second set of outs to the fathom sub. additionally, i ran the subwoofer out from the HT pre/pro to the second inputs on the fathom. i made sure the XOver point in the pre/pro was set higher than on the fathom and everything seemed to be fine. Do not get too hung up on finding a preamp with HT Bypass, as any preamp will do, you’ll just have to remember to run the volume up when you select the input from your HT pre/pro.

best to call JL Audio and speak to their tech (Barry) about your specific system. i've also talked with the tech at SVS and they suggested the same setup the JL did, noting no damage would occur.

Another option you might consider are Rythmik subs. they are FANTASTIC and their DI amp option (soon to be replaced by the PEQ3) is specifically designed to work with both a 2-channel preamp and a HT pre/pro.

to your comment on high end pre/pros, my aesthetix calypso was night and day better than my theta casablanca. to my surprise, using my Wyred4Sound DAC2 as a preamp was also better than the casablanca and very close to the aesthetix.

Srosenberg, thanks much for the input. I actually did have an email exchange with Barry at JL and he confirmed what you said, its perfectly fine to run both inputs, LFE/RCA out from pre/pro and balanced/XLR out from preamp.
Not surprised your calypso was better, as I have heard great things about that unit, but VERY surprised about the W4S being so good. What gear are you running? Wondering if there is a certain threshold of gear quality above which such distinctions become more pronounced. I'm running B&W N803 as mains (HTM1 ctr and DS7 surrounds), with Sunfire TGA5200 amp ( a very good and underappreciated amp) and a Sunfire TGP5 pre/pro fed by both a modded Denon 3930ci and a Sonos-BelCanto Dac2 combo. Although not heavy high end, would assume its good enough to hear a difference?