How to optimize sub integration with 2 channel?

Some sub mftrs.  will let you run signal to the sub first, then use the crossover in the sub to send signal containing frequencies above the sub crossover point to the main speakers.  I've have seen this approach criticized however (crossover in sub is not very sophisticated???).  

Most subs just have a low pass filter, and allow the main speakers to play at full range. This makes integration relatively easy. Other subs, however, also have a high pass filter for the main speakers, allowing you to relieve the main speakers from the stress of having to reproduce the lowest frequencies. The price for that, however, is more complex integration.
If the sub of your choice does not have an inbuilt high pass filter (these days few do), you will have to use an external cross over/high pass filter. Interestingly, many pro audio amplifiers have precisely such a high pass filter. And some of those pro audio amplifiers are very good, at least as good as some audiophile amps, though for much less money (thanks to economies of scale and lower mark ups). So that may be one way of doing this. Another far more expensive way would be to get the forthcoming DSPeaker X4 DAC/Preamp/crossover/room eq.
In any case, with subs I would always recommend having at least two (in mono) for a smoother in-room response, augmented by dsp room eq like the Antimode 8033.

Since OP's PrimaLuna Dialogue HP tubed integrated does not has pre-out/power amp-in, high pass filter will be limited to speaker level connection. 

If you do not wish to use a high pass / EQ for the main speaekrs there IS a cheat you can use. :) Stuff the ports, converting them into sealed speakers. This will give them a higher cut-off than normal and increase power handling.

This will also make subwoofer integration a little easier. Of course, many audiophiles swear sealed speakers are better sounding no matter what.

Having said all of that, you really should wait for your speakers to arrive, and figure out your placement, etc. I love my sub but I end up using it only for movies.

Best,

E

@willemj . thanks for info on hi pass filters and XOs. 
that is my weak point. need to do some research. 
Im interested in the Zu Audio Undertone Sub:

I am interested in this sub: the Zu Audio Undertone subwoofer http://www.zuaudio.com/subs/undertone.
It does say there is a Signal Processing Bypass, but I dont know how it works.

here is a pic of the backside, and connections options: 
From Zu's website:

 "Line-Level Input: yes, RCA (left and right summing)
Sub Line-Level Input: yes, RCA
Speaker-Level Input: yes, 5-way binding posts (L/R summing)
Tunability: yes, very
Signal Processing Bypass: yes, switched for those that want to integrate more elaborate signal processing but desire to take advantage of the excellent amplification of Undertone."

Also: from Zu website, "It is a down-firing subwoofer with active signal processing and built in amplification. It accepts line-level feeds (RCA left and right summing), sub feed (RCA) and speaker-level (five-way binding posts, left and right transformer isolated and summing)."

Here is the best image I could find for the back of the sub, and its connections/options: 
https://static1.squarespace.com/static/51dd8a95e4b0ff2f7c9874ae/59e64781f43b55b96d873030/56d0d5d286d...