With that receiver they should be set to small and crossed at 80hz. You have a couple different ways to approach this problem.
1. Upgrade your sub to a ported design, maybe 2.
2. Add another vanquish.
3. Add a mid bass module.
4. Upgrading your receiver to one with pre-outs, if you like Pioneer get an Elite. This will allow you to add a separate amp to drive the RC70's and center. You could then set the L/R & C to large and set the sub to Plus.
Going this route...