I don't know about the Ayre house sound, but the QB9 DAC as compared to many of the DACs out there is beautiful, slightly romantic and polite. All things that other people have said.
It's a fine sounding DAC, striking a nice balance between resolved and musical. For some systems, it may be just what the doctor ordered.
I've also auditioned or owned the W4S DAC2 (a bit on the bright side), PWD MK2 (smooth and undigital), NAD M51 (resolved, neutral, but not fatiguing at all, great direct to amp too), and a number of other DACs.
I'd put the PWD MK2, Ayre QB-9 and NAD M51 all in the same class. Their appropriateness separated mostly by personal preference and system synergy.
I'm a big fan of the M51 right now. I've never really thought too much of NAD components, but the M51 has really changed my mind.