My experience in regards to bass extension with the ARC SP-16 is on point with Mapman's. It may well be possible to get more bass out of my system, but I am not missing it. The bass that is there is tight and under control, more so than with other amp/pre combos I have tried. For the record, I have not tried much and those that have been tried were lower grade than the ARC for sure.
However, I believe that my system's bass performance has more to do with the room gear interaction than the specific gear. I have a small space, to much bass would overwhelm the room. Another way to phrase it is I maybe satisfied now, but if I moved to a larger room I might not be.