First Are you agreed with me that by a supply voltage of +-28V and a load impedance of 4 ohms, The output power of the LM3886 is 68W?
If so, Please consider that +-28V means 56V total supply,. the peak to peak voltage across the 4 ohms load at 68W output power as I calculated in my previous post is 46.64V (Vp-p = 2 x 1.414(sqrt P x R) = 46.64V).
It reflects that by having a 56V supply voltage the the P-P output voltage which you can expect is 46.64V, So the lose is:
56V - 46.64V = 9.36V.
So by 56V supply voltage you will not get any voltage larger than 46.64V in the output, So that output voltage is the reference voltage for calculating the clipping/ going to saturation state. for instance by a gain of 21 the MAXIMUM P-P input voltage must be 46.64/21 = 2.2. any higher p-p input voltage larger than 2.2V causes the output to go to saturation, Right? Unless you say That the chip is able to provide more power than 68W by a supply volatge of +-28V?!