1st time SUB set up option & LFE db levels through receiver

[Collectors Set]

Any input appreciated.

12" Sub has been successfully zapped and added via the Audyssey mic to an Onkyo receiver.

On the Sub itself, there is a switch setting for Pro Logic or Dobly Digital 5.1/7.1. If I go with the Pro Logic option, I believe the receiver totally runs it. If I go with the other option, I have to manually tweak the settings all the time. Maybe this is an obvious dumb question, but what would you choose and why??

On the Sub itself, I have a good idea of the cross over frequency and volume controls of where I want it to be, but noticed something in the online screen audio setup menu for the Onkyo receiver and the instruction manual really does not address very well. There is a dedicated LFE menu section with a grocery like list of each audio codec type [Dolby HD, DTS HD, etc.] and each with its own db rating. Currently the values are all zero. Looks like they go in increments of 10 db. The lowest rating I can choose is -20. What would say to do with this section -- do I want this number low or high??

Thanks