How to optimize sub integration with 2 channel?


I’m at the point of wanting to integrate a proper sub into my 2 channel system.

Hey folks,
I understand that I can control the gain and frequency of the low end of the sub,via the sub.

But is there a way to do the inverse? Can I reduce the low end of the speakers to about 45 hz and use
the sub instead from about 44 hz and below?

If possible, how would that work? e.g., use an external crossover for the floor standers?
The problem is that there is too much output at around 3-50 hz if I use both the speakers and the sub.

thanks!! Gary

Rig: (Bel Canto DAC–> PrimaLuna Dialogue HP tubed integrated–>
Dali Helicon 400 floor standers, Spatial M3 Triode Masters, and coming soon Dynaudio S3.4 Contours (thanks Joe)
128x1281graber2
Subwoofers can be as small as they are by using big amplifiers and using them to boost the signal, the lower the frequency. However, there are limits to this if you do not want to have too much distortion, or destroy the driver. Therefore, increasingly subs have complex dsp to do this without overpowering the driver. So maximum spl is monitored, and so is frequency response. Not sure what the Zu does exactly, but my B&W PV1d reduces the low end extension more and more, the louder you play it, to keep the driver within comfortable limits. So there is little point in bypassing this. It does not look like the Zu dsp has anything to do with dsp room equalization of the kind built into e.g the bigger Velodyne subs.
High passing a sub only makes sense in two very specific situations. The first is if you cannot play the system loud enough, either because your amplifier does not have the power, or because the speaker cannot handle more power. If that is the case, highpassing the main speakers and main amp makes their life a bit easier. The second issue is related, if the speaker distorts too much when played loud. Speaker designers can increase low fequency extension, but at the expense of increased distortion. If you do not like the balance that was struck by the speaker’s designer, reducing the burden on the main speakers helps. In short, in normal situations I do not think there is much point in high passing the main speakers, given the disadvantages. And I would certainly not want to spend big money on addressing the shortcomings of an amplifier or speakers.
The Zu looks like a pretty ordinary though perhaps a bit expensive subwoofer. But I have never heard it, nor would I think that a listening test would have helped me much. Subwoofer sound is largely determined by the room they are in, and by the room modes in that room. Listen to them in a demo room, and you have heard the sound of the demo room rather than of the sub. It is for that same reason that I think multiple smaller subs are far preferable, because they smoothen the response, and even so preferably combined with dsp room equalization by a unit like the Antimode 8033. See here for some introduction: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti...
For that reason, you may want to consider the Audiokinesis Swarm System, but always in combination with dsp room eq.
Why don't you call up  or email Zu and get their take on it?
From my experience, they are very communicative about their products.
Bob
Just discovered that the Swarm system also includes the possibility of high passing the main speakers.
@1graber2
The PrimaLuna has a mono out that is used for the sub. I’m not sure if it is the best solution, but I Currently use a single RCA cable to run from the Mono out of the PrimaLuna to the LFE in my current sub (a 10 year old Martin Logan Grotto, 10", 200-250 watts or so).

Also, the PrimaLuna does have an HT Bypass that only uses the Amp section of the PrimaLuna. Is that what you mean?
If you want to high passing the main speakers, you need a subwoofer with speaker level high pass filter like this one:
http://www.apexjr.com/images/MK1250amp.jpg

If you want to apply line level high pass filter via HT Bypass, you need a separate preamp to do that.
Since you already have a sub, I would suggest getting a DSpeaker Antimode 8033 first, for room equalization. You will be pleasantly surprised by the improvement. See here for a review: http://www.theabsolutesound.com/articles/dspeaker-anti-mode-8033-dsp-subwoofer-equalizer-tas-204/
I am not quite sure about the kind of connections you have, but if you have a line level output from your amplifier, that should work just fine. Get the 8033 Cinema in that case.