replacing my audio system sl320 1997

my amplifier is going bad on my bose system in my 1997 SL320.
Looking at aftermarket and am close to settling on the Kenwood excelon
I am told that the subwoofers used in the bose are not replaceable in the current location and I'll need a subwoofer mounted in the (already small) trunk.
Has anyone else faced this problem. It appears that Kenwood makes a 7inch subwoofer that has an adapter to convert to 6.5 inches which is, I am told, the size of the current Bose--don't know depth.
any advice appreciated.
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