The official answer from B&O is to disable L/R speakers in the Theatre. You’ll get muddy separation otherwise. However, play with it both ways and see how it sounds. Nothing stopping you from experimenting.

Change the theatres L/R to act as Sub centre. I did and works great.

First of all, thank you all for your professional responses.I’ll try out different configurations and see which one best fits my preferences. I have one more question:In my current setup, the three-piece system is centered around the Theatre.How can I tell whether the Beolab 8s are operating in "wide" or "narrow" sound mode when they are working in sync with the Theatre? Also, if I adjust the sound settings of the Beolab 8s individually, will that affect the overall settings of the main three-piece setup? Thank you

Sorry for the delayed response to this old post.  I just picked up a Theatre about a month ago and only found this forum recently. I understand that you're using your BeoLab 8's as front speakers.  I think you could get much better use out of your pair of BeoLab 8's if you set them up as side or rear speakers. I purchased a BeoAmp2 and have been playing around with testing a pair of speaker in different positions.  With just one set of speakers to add to the Theatre, I really feel that adding them as sides or rears provides the most immersive sound.  I currently have a pair of speakers positioned just to the sides and slightly behind my viewing/listening positions.  After positioning those speakers and running the room setup routine, the sound seems to just seamlessly wrap around you. I just purchased two pairs of in-ceiling speakers and a couple more BeoAmp2's that I will be setting up as front and rear height speakers.  I'm hoping those height speakers will greatly improve the overall sound in my home theater. I'm not sure if I will ever purchase front speakers.  The Theatre's left and right front channels seem to do a great job.  It seems the only benefit that I'd get from adding front speakers would be just to widen that front sound stage.  Personally it's going to be hard for me to add front speakers, because at that point I'd only be using 2 of the 12 speakers in the Theatre and I'd end have a very expensive 2-speaker center channel system whose primary function would just be surround sound processing. The picture you shared of your setup looks very nice.  I'm in the process of building out something similar in the front of my home theater.

I have a similar setup and I recommend the above OR get some older B&O speakers like the BL3 or BL12.3 to use as rears.  The 8's are amazing but they won't be used to their full potential as a rear so its a slight waste.

I haven't heard the BeoLab 8's in person.  Do the 8's used as front speakers provide significantly better sound quality than the Theatre on it's own?  On paper, the left/right front speakers in the Theatre seem pretty comparable to the 8's.  I've been assuming that I would need to jump up to the 28's to significantly improve the sound quality for my front channels. I love the looks of the BeoLab 8's, but I'm having a hard time justifying $9K for side speakers.  B&O is running a surround sound sale right now that would knock about 15% off of a pair of 8's which makes it a little more palatable.  Not having heard the 8's, I just can't pull the trigger on this purchase and I'm not willing to fly across the country to visit my closest B&O reseller to give them a listen.  I find myself missing the 80's and 90's where there were B&O dealers in most decent sized cities.  

It's not that the BL8's sound better than the theatre. It's just the theatre sounds better if you made the stage wider with really any B&O Speakers.  It's easy to think the front LR speakers are just making the stage "wider" but its really just adding more of an immersive environment over all. So really what people are recommending is that with your current setup the 8s in the back will make things sound more immersive but adding anything to the front of the theatre would also help a lot.

Over the past few months I've added 10 additional speakers and a subwoofer to my Theatre setup (now 7.1.4).  I've been playing around with speaker placement and testing different assigned speaker roles and I have some thoughts to share on the original question posted here:

• Now that I’ve added the two Beolab 8s as front speakers, should I disable the left and right channels of the Beosound Theatre? Or should I assign them to take on the role of the center channel?  My main concern is whether disabling them would be a bit of a waste. And if I don’t disable them—whether keeping them as left/right or assigning them to the center channel—would that cause any conflict with the Beolab 8s, possibly affecting the overall sound quality and performance?

Adding external front speakers has definitely "widened" the front sound stage.  Not wanting 10 of the 12 Theatre speakers to go to waste, I initially tried doubling up the front left/right speakers by assigning those roles both to the Theatre and external front speakers.  For moving watching, this setup doesn't seem to change the sound much to me (it's neither a negative or a positive change), but for listening to music I found that this configuration actually made music sound slightly worse.  I'm not sure if that configuration was causing some type of sound cancelation or not, but I quickly stopped assigning multiple front left/right speaker roles. I do find that assigning the Centre speaker role to the Theatre's Left Front-firing, Centre Front-firing and Right Front-Firing speakers provides a better center channel experience in my room.  With those 8 speakers assigned to the Centre role, I find the sound to be more impactful and voices are clearer when watching movies. I ended up assigning the Theatre's Left Side-firing and Right Side-Firing to the L and R front speaker roles to help widen my front soundstage even more.  For my room, adding these additional speakers to the L and R front speaker roles has improved the sound and widened it even more, but that may be because of my room setup.  I have my Theatre setup in a corner of my family room.  That corner is not a standard 90 degree corner, it is a bit wider at 124 degrees, so there isn't as direct of a reflection as there would be in a more standard room. Even though I have 4 ceiling mounted height speakers I ended up assigning the Theatre's Left and Right Up-firing speakers to the L & R Front Height speaker roles, doubling up those assignments with 2 of my external height speakers.  In the two primary seating positions that I measured from, these additional assignments don't make any noticeable difference to the sound, but in the farthest left/right seating positions they do help deliver the front heigh audio.  I think this only helps my room setup because my seating positions span just over 20 feet in width.  The two primary seating positions are in the center of that 20 foot span and I have the four LCR ceiling mounted speakers aligned to direct sound right in the middle of those two primary seating positions. So far I'm very happy with this 7.1.4 setup.  Watching movies with good ATMOS tracks is an incredibly immersive experience.  I've also found this setup is exceptional for music listening, especially with all the ATMOS enabled audio tracks available on Tidal.

Thank you for sharing your findings/your setup. I am sure this can be helpfull for many ‘Theatre-users’ - a lot of inspiring stuff there. MM