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

Bob, OK, so you are firmly in the camp of processed sound, if done right, sounding better. I'm ok with that (I think Kal at Stereophile agrees with you too). Of course I cant agree or disagree as I've not compared it much, but assume you have and to your ears processed is better? Clearly there are two distinct camps on this, and as always, only your own ears will tell you what you like. Some people firmly believe that room correction is the only way to hear music properly. However, I think the argument on pre/pro vs preamp assumes a certain level (pun?) playing field and, given such, a preamp provides a better, cleaner, clearer picture than does an average pre/pro. Again, assumption on my part from reading forums. No doubt that, in a poor room, processing/correction can probably make a bigger difference and provide better SQ than a good preamp.

A pre/pro is a swiss army knife that is great for doing a bunch of stuff at the sacrifice of doing just a couple really well.

I'd prefer a high end preamp/amp and take the extra time to do my own sub integration.

[From the description, it seems that Jeff's original idea of a line level switch box would be a simple solution. Decware's box comes to mind]

No, actually, according to Barry, just connect the two units directly to the sub: pre/pro LFE out via RCA to sub, and preamp L/R out via XLR to sub. Just dont send signals out from both units simultaneously!

Although I am of course not familiar with the internal design of the JL sub, I absolutely can't envision a way in which driving both inputs at once could cause damage to it, assuming that both inputs are not simultaneously overdriven with absurdly high volume signals. My guess is that the reason the manual refers to not using both inputs simultaneously relates to sonics.

First, with both inputs simultaneously connected to different components there conceivably could be an increased chance of ground loop issues arising.

Second, my guess would be that the unbalanced signal input is simply connected directly to one polarity of the balanced input. If so, that would mean that whichever component is providing the input signal that is being used would have to drive a load impedance approximately equal to the output impedance of the component that is connected to the other input. That will be a much lower impedance than line level output stages are normally called upon to drive, and, depending on the design of the particular components, compromised sonics might result. And I suppose that a poorly designed output stage in one of those components might even suffer degraded long-term reliability or damage as a result. Finally, it would mean that the balanced input is no longer truly balanced, because the two signal polarities would be loaded in a very unequal manner.

As far as line level switchboxes are concerned, the DB Systems DBP-2JAU/5 from DB Systems may be of interest. I've had occasion to use one in the past. It is nicely made and does what it is supposed to. It costs $110 for the version with gold-plated jacks. My one concern about that approach would, again, be the possibility of ground loop issues arising.

Regards,
-- Al