2 Channel Subwoofer connection


Hello, I am seeking advice for a Subwoofer connection.  My system consist of a Rotel RCD 1570, Jolida JD 202 Integrated Tube Amplifier and a pair of Bowers & Wilkins 705. This set up is just for music listening.
I like how much detail I get from the music with these 705, the only problems is that my loft is an open space with high ceilings, therefore, the bass is not very strong. I thought I could add a Subwoofer. The issue is that my integrated amplifier doesn't provide a Subwoofer out. The only option will be to run speaker wire from the integrated into the Subwoofer's speaker level inputs, then connect the 705s to the subwoofer's out (As pictured in the diagram)

 https://cloudflare.crutchfieldonline.com/ImageBank/v20160824170200/ImageHandler/scale/978/978/core/l...

However, as I've never attempted this connection, I am concerned this could degrade the audio signal, would the sound quality be affected due all these extra wiring and having the signal go through the subwoofer and then to the 705 monitors?
I've looked into the Bowers & Wilkins ASW750  but this doesn't come with sub's level inputs. I am considering the ASW300 instead. Any advice will be much appreciated.
Thanks,

Joseph







mamifero
Thank you all for the useful advice. I will certainly look into the RELs and the other brands.

A couple of questions though. By keeping the main speakers connected to the amp and then running a second set of wires from the output taps to the sub, there won't be need to adjust the phase adjustment knob correct? 
As it sounds like they will be in sync for what I understand.
Finally, regarding bi-wiring. Currently my main speaker monitors are bi-wired to the amp, should I bi wire to the sub as well?

Here's an alternative option if you can use two subs and your main speakers allow both spade and banana connections.  In my winter system, I use a pair of Gallo TR1D subs.  The subs have a speaker level input.  I run my main speakers full range with the speaker cables terminated with spades which leaves the banana sockets at the speaker unused.  Therefore, I can send the signal to the subs with a short banana terminated cable of the same type as the main speaker cable to each sub directly from the main speaker.  This way I don't place the cross-over of the sub inline with the main speaker.

The cross-over adjustments on the subs still function as regards to the subwoofer outputs but do not limit the signal to the main speakers.

My main speakers are first order and the Gallo subs are sealed.  The subs are placed close to the main speakers and integration is fairly simple.   

I also dislike REL subs FWIW.

Thanks.
With the recommended set ups I would just need a passive sub. However, most subs are active. Does it make any difference to buy an active sub and use it as passive? Would the active sub be on all the time, thus generating unwanted interference, even though it will be used as an active woofer?
With my setup you definitely need active (powered) subs.  The Gallo subs I use automatically go to standby when no signal is present.  They are switchable for full on, full off, or signal switched on/off.
Any subwoofer with high level inputs will work fine.  Just leave your B&Ws wired directly as they are and run two speaker wires to your subwoofer, connecting from the same taps your B&Ws use to the left and right high level inputs on the sub.  I would not wire a passive sub this way as the amp will see the additional load.  Wiring an active sub this way is perfectly OK as the amp sees no additional load.