I agree that the Chapuis won't kick that bad.

Muzzlebreak on a DR--NO WAY!!

Mercury reducers-screw up the balance and handling

A good recoil pad and PACT pad will help immensely-try this first and see what you tolerate.

Past that your left with weird shotgun tricks like Gracoil "shock absorber units" hung off the butt of the stock that compress and prolong the recoil stroke.Don't know if that will even work with a Double.

If you can't handle the recoil of the 9.3 DR with a recoil pad and PACT pad you may just need to go to a smaller caliber.