OK, guys: Here 'tis: My alleged "perfect' solution:
1. Follow the RCS Diagram of the DBL X-over for names, etc. [Do NOT follow their wiring instructions!]
2. You need an Al diamond, wired to the 'hot'/center rail.
3. Rails "1" & "2" are isolated [no connections]
4. You need 4 DZ 1000's [or 2500's]; wired [appropriately] in pairs.
5. You need 2 DZ-1002's [or 2502's]. Each operates the appropriate pair of turnout points.
6. The 2 outside rails between the frogs [those directly above & below the diamond] need to be cut at their mid-points. Connect each of the 4 segments to the appropriate L or R terminal a la` the DZ instructions....Just like you connect a single turnout for non-derail.
7. There are no relays!
Now you have 'everything'.....Both on thru, both on curved, one on thru & the other on curved ------- with no need to be concerned about the other pair. Then just run trains, with no need to worry about re-setting points or derailments!