The Arcam amp is very good.
The B&W would be fine as a match, but I'd go for the bi-pole rear surrounds for the proper movie experience. Here's something I wrote for another member considering the B&Ws...
Rear speakers.... It's easy to overlook just how important they are in creating a convincing and enjoyable surround sound effect.
The whole point of surround sound is to feel like you are immersed in the action, right? So the rear sound field should be enveloping without you being aware of the location of those speakers. That's very different from what the front speakers are doing. Here you want excellent imagery and pinpoint accuracy.
So, if we use direct firing speakers for the front because they give excellent imaging....why use them in the rear where that's exactly what we don't want?
The correct speakers for rear effects use are bi-pole speakers that produce a diffuse surround effect. Who says so? Well Dolby Labs, DTS, THX, all of the worlds theatre dubbing and sound mixing studios and pretty much everyone in the business of making movie soundtracks.
There are times when direct firing speaker are correct for rear use; but it's not for movie surround work. Multichannel SACD- and DVD-Audio music disc should be listened to with direct firing rear speakers. But that's it.
Something else is special about rear speakers. It's how close they are to the seating position.
The front speakers need space to focus the stereo image because that's how they work. Sit too close, or way off to one side or the other and the effect is ruined. Now think about where the rear speakers should be - which is either side of the main seating area and about a foot higher than seated head height. How close are you to those speakers? Are you closer to one than the other? Are you sitting much closer than you'd consider correct if these were front speakers?
Of course, not every room will allow for big boxy direct firing rear speakers to be put in the best position; so what's the alternative? The corners a ceiling height of course!! Now guess what's the worst place you can put a speaker
High corners are bad for various reasons. The first is speaker design. They just aren't tuned for somewhere that messes up the bass as bad as a corner. The second is imaging. We hear direct and reflected sound. The best imaging is where we hear very little reflected sound. Reflections come from hard surfaces; walls, the ceiling and the floor mostly. The further away those surfaces then the less reflected sound to spoil the imaging. A corner puts three hard surfaces right next to the speaker.
Dipole speakers have a slim profile. They protrude very little from the wall. The speakers fire sound along the axis of the wall forwards and backwards. This creates the even and diffuse sound field which is exactly what's needed for rear surround effects.
If you haven't nodded off yet then you might be asking why all rear surround speakers aren't di-poles. The answer in most cases is cost. B&W's di-pole rears (DS3) cost £550 compared to £299 for the 686 direct firing speakers. That would push the budget for a B&W 5.1 system to over £1500, but result would be so much better.
Some alternative brands that do dipole rear surround - Monitor Audio, Focal, Kef, Teufel.
I'd also budget something for a proper video calibration on the projector. That alone will make more difference to your picture quality than spending an extra £1000 on a better projector. Calibration is generally £350-£400, so in that context it is good value.
Speakers - have a listen to Monitor Audio Bronze BX and Silver RX ranges too. There are bi-pole/di-pole switchable rears available in both these ranges.
With an amp & speakers as good as the ones mentioned here they deserve better quality speaker cable than I think you're budgeting.... certainly on the front three speakers at least. Chord Rumour would be completely appropriate. It's around £12/m + termination which is always a good idea at the amp end.
) - a visible sheen over the material in bright scenes. Both of these drove me nuts with past screens.