Hi Bob,
You can audition the 350 with Pat and the 500 at my place then decide. We can always turn off one of the subs. As you know having two 500s gives only 3 db extra sound pressure subjectively (though requires twice the power, of course). Do you plan to get the whole set up now or get them sequentially? I am sure you will be very pleased with the M80s as well either of the subs.
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John
Our HT