I know the Marantz will set to large if it detects a strong enough response below 40 Hz. Uncertain what the threshold is with D&M. But even a small bookshelf that will be giving up the ghost with a full range program can pop Large.
@Rony
I think I get what you are trying to accomplish, but you are working against physics. Specs for your Speaker are a little hard to find. What I saw on one site was a listed bandwidth of 38Hz to 28kHz. No indication if that's -3db or more at its rated extension.
Trying to increase the SPL by boosting the trim and/or push it beyond it's rated extension will not result in a good SQ. It may serve to destroy the Speakers.
Investing in quality Subs and crossing at 80Hz will give you a much more potent experience. Your total open room volume is what will more greatly affect your Bass response. That little PB1000pro is a little trooper, but if you have it in a 5000cu.ft room, it will struggle.