One sub, a two channel system ,one HT reciever ??

It is reasonably simple. When you use the line level in and out you are using the crossover and rolling your main speakers off at the subs crossover point. When you use the speaker outputs you are NOT rolling off the main speakers. In theory the first has the advantage of lessening the load on the main speakers because they no longer have to reproduce low bass. Nevertheless, I find the second method to work much better. I currently have three types of subs [REL, Nelson Reed , and HSU] and have had others in the past. The critical factor is not having to run your signal through the crossover. I have yet to see a crossover that did not degrade the sound. I am assuming that in the first case you are running the pre out to the sub input and the sub output to the power amp in and thus using the subs crossover. Since you did not name your equipment I can't be more specific. If this is not true advise me and I will post further. When hooking up equipment I have always found it helpful to visualize your system as a stream with your signal source at its head. Just follow the stream toward your speakers, hooking it up as you go.

When you use the line level in and out you are using the crossover and rolling your main speakers off at the subs crossover point.

On some equipment this can be a limitation yes. However, I think there are preamps out there that allow you to have control over each speaker individually so the sub can be crossed over or not and the speakers can be crossed over of not.

I'd look into the Anthem D1 or D2 if you want a high quality HT preamp with plenty of flexibility and that could also serve as a source for a decent two channel system or a two channel + sub system.

If your receiver folds the LFE channel into the mains when set to (large mains-no sub)....you can simply add something like the Paradigm X-30 crossover (around $100 used)into the system. (or any other good crossover on the market).

It would connect like this:

Two channel preamp>>Paradigm X-30>>Mains and sub. This sends the fullrange signal from the receiver, to the preamp. The preamp feeds it to the Paradigm crossover. The paradigm crossover filters the mains and subwoofer, or...just the subwoofer if you want to run the mains fullrange. (a second set of preamp outs required or splitter cable for this method).

I don't agree 100% with "Stanwal" on his second choice option being better....but don't really dis-agree 100% either.

Running the mains fullrange, is speaker dependent (the main speakers). The speaker level connection method assumes that the mains have a smooth low freq's response....many small ported designs are anything but. So....this method depends.

I also don't agree with this:

"The critical factor is not having to run your signal through the crossover".

If this were true (critical), we would all be using single driver speaker systems. Sometimes the gains, more than make up for any loss.

Note: My options also depend on a few things.

Dave

My equipment is Kef 104 /2's (with a Kef Kube external line level cross over currently not being used)
Audio Research LS 15
Classe Ca 2200 Power amp.
Yamaha 650 HT reciever.
Velodyne DLS-3750R sub
Levinson transport and Sonic Fronteirs DAC

The Velodyne sub has a variable cross over. Which is now set to off because the HT Reciver is managing the cross over point for HT material.

The reciever has a lfe output which I am using now for HT.

In two channel mode... I just switch inputs on the LS15 and leave the HT equpment off.

So, from what I understand I could do this.

I set the yamaha to large mains and No sub.
Ditch the LFE output to LFE line level input.
connect the sub by going from the power amp to the speaker input left and right of the sub and then from the speaker outputs to the KEF 104's. Then set the cross over on the sub to 120 Hz. Then run the reciever's auto calibration with the main LR channel set to 12 oclock on the volume control. This calibrates all of the surround and .1 channels.

This way I get the benfit of using the sub for music with the bass limited kef's and keep the LFE info from HT material going to the sub as well using the yamaha's processor.

Am I off base here?
Thanks for the reply's