I would have to agree with wid. It sounds to me like you are pushing the limits of the amp and you are now recognizing the 1% distortion they have when bridged in mono mode. To get above the SPL you already achieve from the stock Onkyo amps with clean sound, you need to look at amps with 200W into 8ohm or more.
The M60s can handle just about any amount of power you want to put into them, but the trick, as you are discovering, is to have them still sound clear and for that it takes lots of power.
A rough number from the Crown power calculator, if you are 10 ft away from your speakers and want on avg 95 db from the 89db M60s and you are listening to music with a dynamic range of 10db(a good avg) you will need about 350Watts/ch.
Last edited by jakewash; 12/04/08 08:38 PM. Reason: added some numbers
