77db spl at 31.5hz and 76db at 25hz = old sub, audyssey
71db at 31.5hz and 62db at 25hz = new sub, audyssey
Have you run measurements with Audyssey turned off?
It could be just your different sub and its placement creating a null at 25Hz, phase issue?
The sub itself could have a 30Hz cuttoff setting you are unaware of too
The old sub had a 25Hz BOOST setting that isnt on your new sub and therefore its down quiet a bit....
Many factors could contribute.
Do the tests without audyssey on, if you have not done so to see if its creating that -14dB difference.
btw, thanks for coming here......the Audyssey threads is not the best place for solving issues IMO. Anyone who remotely talks negative about Audyssey in that thread gets thrown to the wolves, its happened to me many times. In the end we just want discussion and answers. There should be zero emotion about the Audyssey product but people are strange in thinking its their baby to protect.
This isnt really a DIY thread either but atleast the passion, knowledge and level headed responses are good