Amp's Line-Out to Subwoofer?

Hey Audiogon forum!

An audiophile acquaintance of mine has been trying to convince me to get a subwoofer for my system recently, and I am curious about the possible benefits. I have a pair of Elac B6's fed by a Music Hall A15.2 (which has no LFE out) and he said I'd be able to use the Music Hall's Line Out output to connect a sub. I have a lot of questions about that. Mainly (and obviously) will that work? Second, if it DOES work, will the full signal be sent to the speakers and would that create any weird complications in sound quality? I've never heard of doing it this way before so I have no clue; I just know that I love my current amp and don't want to get a new one just to get an LFE output.

Thank you!!

Also, here's the Music Hall manual which details the Line Out option in more detail:
Yes that would work.  Whatever sub you get will most likely have all of the crossover and level controls that you would need to match your speakers.

All the line out is doing is sending a full range signal, (controlled by the volume control) to the the device hooked up to it.  Be it an amp or sub or etc.

You really do NOT want a LFE output for a 2 channel system,  because that would require the source to be encoded then decoded by a processor to function properly.  LFE is usually associated with the audio signals from a video system.  Low Frequency Effects are part of that signal chain.
that's what I do, and works fine.  Take the xlr out of the DAC to the sub (use crossover and level adjustment on the sub) and RCA out of the DAC to the main speakers amp.  would be nice to be able to cut some of the lows going to the mains, but it works fine this way also (crossover at 40hz on the sub.)

Just taking a quick look at the manual, I would agree with mofi's response, however, if you look at features here,

it states that the line out is fixed. This means that the signal is not controlled by the a15.2 volume control. Even though the sub would play, it's volume would only change by using the sub volume control.

If the line out is variable, it will work great as mofi described, and the manual seems to imply it is variable, however the website says fixed. If fixed trying to use a sub is not a good idea.

Looks like you need to contact Music Hall.

Thank you, all, for getting back so quickly and helpfully! I will definitely be contacting Music Hall to see if this is a fixed or variable line out (does anyone know why the former would be of any use to someone?). If it's variable, it'll be time to start sub shopping.

Also, I have a cheap Polk sub somewhere that I don't use. Maybe I'll test this output with it and see what happens. 
tls49 is correct, if this is a fixed line out.  However, I really doubt that it is.  It wouldn't make any sense to make it a fixed output?

I would indeed get a hold of Music Hall to make sure.
I found the following comment about the a15.2 that was placed in 2012 at a different forum:
Two years ago they told me they screwed up production on these and hooked up the subwoofer out to the fixed volume instead of a variable volume, but it would be fixed in the future.
I see also that in the successor model, the a15.3, the corresponding output is labelled as a "pre-out" rather than as a "line out." Conceivably "in the future" might have turned out to be in the design of the a15.3.

Good catch by Tony (Tls49).

-- Al

I will definitely be contacting Music Hall to see if this is a fixed or variable line out (does anyone know why the former would be of any use to someone?)
A fixed line output would be useful for connection to a recorder or to an external headphone amp.

-- Al

Thanks Al, and ironically, that comment from the other forum is a little confusing. I assume they meant, it would be corrected in the future.

Good catch once again, Tony!  Until you pointed it out I hadn't even noticed the ambiguity of the word "fixed" as used in the last part of that sentence.  But, yes, I'd feel pretty certain the poster meant "corrected in the future."

Best regards,
-- Al

I sent Music Hall an email and we'll see what they say. This got a lot more confusing than I thought it would... thanks again for all the help!