that's more open air then most people have
Most people don't own Q900s. In addition to top and side clearance, you need a foot or more to the rear, don't forget.
I'm not sure the Q900 is a good match for your volume needs for several reasons. Most people are usually married to their speakers however, for whatever reason, and wont even consider changing them, but instead are confidant they can get the improvement they seek through a different, more powerful receiver, or adding more powerful outboard amps to the existing one. That's a shame. While there is some, slight validity to that approach, it is overall the wrong one in most situations.
There's no amount of money in the world you could spend to buy an outboard amp which plays 10 dB more loudly than what you already have, without shutting down, yet still adheres to the KEF's power handling limits, whereas speakers that are about 10 dB more efficient aren't that different in price from the MSRP of the Q900s.
Are you already using a good, large sub with them and using the LFE mode, not LFE + Main?
Are you listening in a large/dead room or at a greater than average distance?
Are you using them by themselves when the receiver shuts down or is the receiver strenuously attempting to drive other speakers in some surround mode, not stereo?
The KEFs are actually 90 dB/1W/1m efficient, not 91 dB, according to Stereophile, and they dip down way below 8 ohms at some frequencies with 42 degrees of phase shift at 80 Hz, so calling them "8 ohm" is a tad optimistic.
"The speaker's impedance is specified as 8 ohms, but as fig.1 shows, the impedance drops to 4 ohms in the top octaves and to below 4 ohms in the lower midrange, reaching a minimum value of 3.17 ohms at 160Hz."
If that Rush album has strong, sustained energy around 160 Hz [not uncommon with rock music], that hard to do 3.17 ohms impedance could be exactly what's shutting you down.
[The following graph is borrowed from another thread but comes from the same Stereophile article I linked to.]:
Edited by m. zillch - 10/25/13 at 8:27pm
Originally Posted by arnyk