Diamond embeds in the BATT laps, so you can not clean them off and use a different diamond grit. However, you can use both sides, and if you have only one, I’d suggest 3K (for prepolish) on one side, and 60K (for polishing) on the other. You have to take care not to cross-contaminate. You can use something like a coffee filter with the center punched out to prevent the 3K from contaminating the platen.
As long as you stick to polish, the Darkside laps can be cleaned and another oxide used. You can use diamond polish as well. Originally, for diamond, the rule was to clean the lap, then wipe with oil to repolarize for diamond, but that may not be necessary with the new water-compatible diamond polishes from Gearloose.
The Nubond 1200 works well for prepolish, but it will wear out more quickly than the Darkside or BATT. I’ve never used the coarser Nubonds.