Clive,
Yes, the Yamaha relies on having parallel side walls or it doesn't work properly.
Mirage builds decent speakers (I owned a pair of Mirage bipolar slabs for years) but with Mirage's omni or bipolar approach, you trade off neutrality and accuracy (which you get from Axiom) for the larger-than-life soundstage. I also disagree totally with Mirage's omni center channel speakers, which make for murky dialog, inhibiting clarity.
For your room, add two pairs of QS8 surrounds and you'd have wonderfully immersive surround, coupled with the precise soundstage from some M60 towers and a VP150 center for excellent dialog clarity.
Regards,
