CY has it right but I think you reversed the order of your preamps. Come out of your Sherwood from the L/R front main preamp outputs (hopefully that model has this feature) and run them into one of the inputs on your Grant preamp. Run your CD player into the Grant and the DVD into the Sherwood. Connect the Grant to your Acurus amp and you're set. I believe your idea of a 'Y' adapter with an a/b switch for your M&K subwoofer will work fine (down the road you can hook them both to a Creek obh 12 unit and get the a/b switching plus remote control for your sub).
You are going to have a mess of cables running everywhere though. Good luck.
You are going to have a mess of cables running everywhere though. Good luck.